Ran into BUG() while doing madvise(REMOVE) testing.  If we are punching a
hole into shared memory segment using madvise(REMOVE) and the entire hole
is below the indirect blocks, we hit following assert.

            BUG_ON(limit <= SHMEM_NR_DIRECT);
Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
Forwarded-by: Jordan Neumeyer
Signed-off-by: Adrian Bunk <bunk@stusta.de>