x86/asm: Use "m" operand constraint in WRUSSQ asm template

The WRUSSQ instruction uses a memory operand, so use "m"
operand constraint instead of forcing usage of pointer
register using "r" constraint. The generated assembly
code improves from:

   6ece3:	48 8d 43 f8          	lea    -0x8(%rbx),%rax
   ...
   6eceb:	66 48 0f 38 f5 18    	wrussq %rbx,(%rax)

to:

   6ecea:	66 48 0f 38 f5 43 f8 	wrussq %rax,-0x8(%rbx)

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20240319171714.76342-1-ubizjak@gmail.com