powerpc/align: Use #ifdef __BIG_ENDIAN__ #else for REG_BYTE

powerpc/align: Use #ifdef __BIG_ENDIAN__ #else for REG_BYTE

Sparse complains that it doesn't know what REG_BYTE is:

  arch/powerpc/kernel/align.c:313:29: error: undefined identifier 'REG_BYTE'

REG_BYTE is defined differently based on whether we're compiling for
LE, BE32 or BE64. Sparse apparently doesn't provide __BIG_ENDIAN__ or
__LITTLE_ENDIAN__, which means we get no definition.

Rather than check for __BIG_ENDIAN__ and then separately for
__LITTLE_ENDIAN__, just switch the #ifdef to check for __BIG_ENDIAN__
and then #else we define the little endian version. Technically that's
dicey because PDP_ENDIAN is also a possibility, but we already do it in
a lot of places so one more hardly matters.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>