gfs2: gfs2_evict_inode clarification

When function evict_should_delete() returns SHOULD_DEFER_EVICTION, gh is
never initialized, but that isn't obvious; if it did initialize gh and
then return SHOULD_DEFER_EVICTION, gfs2_evict_inode() would fail to
release it.  To clarify the code, change gfs2_evict_inode() to always
check if gh needs to be released, no matter what evict_should_delete()
returns.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>