x86: atomic_32.h: Fix kernel-doc warnings

Fix kernel-doc warnings in atomic_32.h:

  Warning(arch/x86/include/asm/atomic_32.h:265): No description found for parameter 'ptr'
  Warning(arch/x86/include/asm/atomic_32.h:265): Excess function parameter 'v' description in '__atomic64_read'
  Warning(arch/x86/include/asm/atomic_32.h:305): Excess function parameter 'old_val' description in 'atomic64_xchg'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
LKML-Reference: <4A3467E6.6010907@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>