[GFS2] Function meta_read optimization

This patch optimizes function gfs2_meta_read.  Basically, gfs2_meta_wait
was being called regardless of whether a disk read was requested.
This just pulls that wait into the if that triggers the read.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>