[POWERPC] spufs: Get rid of spufs_coredump_num_notes, it's not needed if we NULL terminate

The spufs_coredump_read array is NULL terminated, and we also store the size.
We only need one or the other, and the other arrays in file.c are NULL
terminated, so do that.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>