gfs2: move quota_init qc iterator increment

gfs2: move quota_init qc iterator increment

Move qc++ from the loop body into the for-loop increment
expression in gfs2_quota_init().

This keeps iterator progression explicit and avoids mixing pointer
advance with duplicate-slot handling in the loop body.

Signed-off-by: Jie Wang <jie.wang@intel.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>