[PATCH] JFS: return correct error when i-node allocation failed

I have seen confusing behavior on JFS when I injected many intentional
slab allocation errors. The cp command failed with no disk space error
with enough disk space.

This patch makes:

- change the return value in case slab allocation failures happen
  from -ENOSPC to -ENOMEM

- ialloc() return error code so that the caller can know the reason
  of failures

Signed-off-by: Akinobu Mita <mita@miraclelinux.com>
Signed-off-by: Dave Kleikamp <shaggy@austin.ibm.com>
(cherry picked from 2b46f77976f798f3fe800809a1d0ed38763c71c8 commit)