x86/fpu: Cleanup variable shadowing

Addresses: warning: Local variable 'mask' shadows outer variable

Remove extra variable declaration and switch the bit mask assignment to use
BIT_ULL() while at it.

Fixes: 522e9274 ("x86/fpu: Deduplicate copy_uabi_from_user/kernel_to_xstate()")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/202204262032.jFYKit5j-lkp@intel.com

arch/x86/kernel/fpu/xstate.c

@@ -1233,7 +1233,7 @@ static int copy_uabi_to_xstate(struct fpstate *fpstate, const void *kbuf,
 	}
 
 	for (i = 0; i < XFEATURE_MAX; i++) {
-		u64 mask = ((u64)1 << i);
+		mask = BIT_ULL(i);
 
 		if (hdr.xfeatures & mask) {
 			void *dst = __raw_xsave_addr(xsave, i);