[DLM] fix loop in grant_after_purge

The loop in grant_after_purge is intended to find all rsb's in each hash
bucket that have the LOCKS_PURGED flag set.  The loop was quitting the
current bucket after finding just one rsb instead of going until there are
no more.

Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>