gfs2: Pass sdp to gfs2_adjust_quota

Before this change function gfs2_adjust_quota's first parameter was an
gfs2_inode pointer. But it always pointed to the quota inode. Here we
switch that to pass the superblock pointer, sdp, so it is easier to read
the code and understand that it's only dealing with the quota inode.

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