x86, asm: Use a lower case name for the end macro in atomic64_386_32.S

Use a lowercase name for the end macro, which somehow fixes a binutils 2.16
problem.

Signed-off-by: Luca Barbieri <luca@luca-barbieri.com>
LKML-Reference: <tip-30246557@git.kernel.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>