GFS2: Use variable rather than qa to determine if unstuff necessary

In the future, the qadata structure will be eliminated and merged
back in with the block reservation structure, after we extend the
lifespan of that. This patch is a step forward in eliminating the
qadata structure. It adds a variable to the do_grow function to
determine when unstuffing is necessary, and has been done.

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