xfs: Add error handling for xfs_reflink_cancel_cow_range

In xfs_inactive(), xfs_reflink_cancel_cow_range() is called
without error handling, risking unnoticed failures and
inconsistent behavior compared to other parts of the code.

Fix this issue by adding an error handling for the
xfs_reflink_cancel_cow_range(), improving code robustness.

Fixes: 6231848c ("xfs: check for cow blocks before trying to clear them")
Cc: stable@vger.kernel.org # v4.17
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Signed-off-by: Carlos Maiolino <cem@kernel.org>