librtas: return CALL_AGAIN on RC_BUSY status in handle_delay()

There is no need to delay before retrying on RC_BUSY return status. The
kernel used to get this wrong too.

torvalds/linux@38f7b70

Excerpt referenced from above commit:

RTAS_BUSY (-2): RTAS has suspended a potentially long-running operation in
order to meet its latency obligation and give the OS the opportunity to
perform other work. RTAS can resume making progress as soon as the OS
reattempts the call.

To avoid uselessly sleeping update handle_delay() to return CALL_AGAIN
immediately when it is passed RC_BUSY.

Suggested-by: Nathan Lynch <nathanl@linux.ibm.com>
Signed-off-by: Tyrel Datwyler <tyreld@linux.ibm.com>

librtas_src/syscall_calls.c

@@ -75,8 +75,8 @@ unsigned int handle_delay(int status, uint64_t * elapsed)
 		for (ms = 1; order > 0; order--)
 			ms = ms * 10;
 	} else if (status == RC_BUSY) {
-		/* Regular Delay */
-		ms = 1;
+		/* Retry */
+		return CALL_AGAIN;
 	} else {
 		/* Not a delay return code */
 		return 0;