remove handle_mm_fault export

Now that arch/powerpc/platforms/cell/spufs/fault.c is always built in
the kernel there is no need to export handle_mm_fault anymore.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>