[RISCV] Update SiFive VCIX documentation link. NFC (llvm#96986)

The previous version of the document did not prefix the intrinsic names
with `__riscv_`. That has been corrected now. We have always implemented
the intrinsics with the `__riscv_` prefix so now the documentation
matches our implementation.

The document is now labeled as 1.1, but I have not changed the extension
version in the compiler since it was only changing the intrinsic names.

llvm/docs/RISCVUsage.rst

@@ -330,7 +330,7 @@ The current vendor extensions supported are:
   LLVM implements `version 1.0.0 of the VTx-family custom instructions specification <https://github.com/ventanamicro/ventana-custom-extensions/releases/download/v1.0.0/ventana-custom-extensions-v1.0.0.pdf>`__ by Ventana Micro Systems.  All instructions are prefixed with `vt.` as described in the specification, and the riscv-toolchain-convention document linked above.  These instructions are only available for riscv64 at this time.
 
 ``XSfvcp``
-  LLVM implements `version 1.0.0 of the SiFive Vector Coprocessor Interface (VCIX) Software Specification <https://sifive.cdn.prismic.io/sifive/c3829e36-8552-41f0-a841-79945784241b_vcix-spec-software.pdf>`__ by SiFive.  All instructions are prefixed with `sf.vc.` as described in the specification, and the riscv-toolchain-convention document linked above.
+  LLVM implements `version 1.1.0 of the SiFive Vector Coprocessor Interface (VCIX) Software Specification <https://sifive.cdn.prismic.io/sifive/Zn3m1R5LeNNTwnLS_vcix-spec-software-v1p1.pdf>`__ by SiFive.  All instructions are prefixed with `sf.vc.` as described in the specification, and the riscv-toolchain-convention document linked above.
 
 ``XSfvqmaccdod``, ``XSfvqmaccqoq``
   LLVM implements `version 1.1.0 of the SiFive Int8 Matrix Multiplication Extensions Specification <https://sifive.cdn.prismic.io/sifive/1a2ad85b-d818-49f7-ba83-f51f1731edbe_int8-matmul-spec.pdf>`__ by SiFive.  All instructions are prefixed with `sf.` as described in the specification linked above.