xfs: free xfs_busy_extents structure when no RT extents are queued

xfs: free xfs_busy_extents structure when no RT extents are queued

kmemleak occasionally reports leaking xfs_busy_extents structure
from xfs_scrub calls after running xfs/528 (but attributed to following
tests), which seems to be caused by not freeing the xfs_busy_extents
structure when tr.queued is 0 and xfs_trim_rtgroup_extents breaks out
of the main loop.  Free the structure in this case.

Fixes: a3315d11305f ("xfs: use rtgroup busy extent list for FITRIM")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>