x86: coding style fixes to arch/x86/kernel/syscall_64.c

After the patch:
total: 0 errors, 1 warnings, 29 lines checked

no code changed:

arch/x86/kernel/syscall_64.o:
   text    data     bss     dec     hex filename
   2304       0       0    2304     900 syscall_64.o.before
   2304       0       0    2304     900 syscall_64.o.after
md5:
0fdbb875cde8892296585226b92f4333  syscall_64.o.before.asm
0fdbb875cde8892296585226b92f4333  syscall_64.o.after.asm

Signed-off-by: Paolo Ciarrocchi <paolo.ciarrocchi@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>