atomic: fix atomic_long_cmpxchg/xchg for 64 bit architectures

On a linux-next allyesconfig build:

kernel/trace/ring_buffer.c:1726:
	warning: passing argument 1 of 'atomic_cmpxchg' from incompatible pointer type
linux-next/arch/s390/include/asm/atomic.h:112:
	note: expected 'struct atomic_t *' but argument is of type 'struct atomic64_t *'

atomic_long_cmpxchg and atomic_long_xchg are incorrectly defined for 64
bit architectures.  They should be mapped to the atomic64_* variants.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>