[POWERPC] Off-by-one in /arch/ppc/platforms/mpc8*

A find -iname \*.[ch] | xargs grep "> ARRAY_SIZE(" revealed several
incorrect usages of ARRAY_SIZE in the mpc drivers.  The last element in the
array is always ARRAY_SIZE()-1, this patch modifies the bounds checks
accordingly.

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Cc: Vitaly Bordug <vbordug@ru.mvista.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>