rust: cleanup unnecessary casts

With `long` mapped to `isize`, `size_t`/`__kernel_size_t` mapped to
usize and `char` mapped to `u8`, many of the existing casts are no
longer necessary.

Signed-off-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Link: https://lore.kernel.org/r/20240913213041.395655-6-gary@garyguo.net
[ Moved `uaccess` changes to the previous commit, since they were
  irrefutable patterns that Rust >= 1.82.0 warns about. Removed a
  couple casts that now use `c""` literals. Rebased on top of
  `rust-next`. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

rust/kernel/print.rs

@@ -107,7 +107,7 @@ pub unsafe fn call_printk(
     // SAFETY: TODO.
     unsafe {
         bindings::_printk(
-            format_string.as_ptr() as _,
+            format_string.as_ptr(),
             module_name.as_ptr(),
             &args as *const _ as *const c_void,
         );
@@ -128,7 +128,7 @@ pub fn call_printk_cont(args: fmt::Arguments<'_>) {
     #[cfg(CONFIG_PRINTK)]
     unsafe {
         bindings::_printk(
-            format_strings::CONT.as_ptr() as _,
+            format_strings::CONT.as_ptr(),
             &args as *const _ as *const c_void,
         );
     }

rust/kernel/str.rs

@@ -189,7 +189,7 @@ impl CStr {
         // to a `NUL`-terminated C string.
         let len = unsafe { bindings::strlen(ptr) } + 1;
         // SAFETY: Lifetime guaranteed by the safety precondition.
-        let bytes = unsafe { core::slice::from_raw_parts(ptr as _, len as _) };
+        let bytes = unsafe { core::slice::from_raw_parts(ptr as _, len) };
         // SAFETY: As `len` is returned by `strlen`, `bytes` does not contain interior `NUL`.
         // As we have added 1 to `len`, the last byte is known to be `NUL`.
         unsafe { Self::from_bytes_with_nul_unchecked(bytes) }
@@ -248,7 +248,7 @@ impl CStr {
     /// Returns a C pointer to the string.
     #[inline]
     pub const fn as_char_ptr(&self) -> *const crate::ffi::c_char {
-        self.0.as_ptr() as _
+        self.0.as_ptr()
     }
 
     /// Convert the string to a byte slice without the trailing `NUL` byte.
@@ -838,7 +838,7 @@ impl CString {
         // SAFETY: The buffer is valid for read because `f.bytes_written()` is bounded by `size`
         // (which the minimum buffer size) and is non-zero (we wrote at least the `NUL` terminator)
         // so `f.bytes_written() - 1` doesn't underflow.
-        let ptr = unsafe { bindings::memchr(buf.as_ptr().cast(), 0, (f.bytes_written() - 1) as _) };
+        let ptr = unsafe { bindings::memchr(buf.as_ptr().cast(), 0, f.bytes_written() - 1) };
         if !ptr.is_null() {
             return Err(EINVAL);
         }