x86, alternatives: Fix one more open-coded 8-bit alternative number

Fix a missing case of an 8-bit alternative number, buried inside an
assembly macro.
Signed-off-by: NH. Peter Anvin <hpa@linux.intel.com>
Reported-by: NYinghai Lu <yinhai@kernel.org>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <4C3BDDA3.2060900@kernel.org>

arch/x86/lib/copy_user_64.S

@@ -29,7 +29,7 @@
 	.align 8
 	.quad  0b
 	.quad  2b
-	.byte  \feature			/* when feature is set */
+	.word  \feature			/* when feature is set */
 	.byte  5
 	.byte  5
 	.previous