m68knommu: fix pread/pwrite defines

Fix system call defines for system call 180 and 181 to match the underlying
system call table function entries.  System call 180 calls sys_pread64, and
181 calls sys_pwrite64, so make the definitions match.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>