gfs2: fix flock panic issue

Commit 4f656367 ("Move locks API users to locks_lock_inode_wait()")
moved flock/posix lock identify code to locks_lock_inode_wait(), but
missed to set fl_flags to FL_FLOCK which will cause kernel panic in
locks_lock_inode_wait().

Fixes: 4f656367 ("Move locks API users to locks_lock_inode_wait()")
Signed-off-by: Junxiao Bi <junxiao.bi@oracle.com>
Signed-off-by: Bob Peterson <rpeterso@redhat.com>