xprtrdma: Update documenting comment

Clean up: If reset fails, FRMRs are no longer abandoned, rather
they are released immediately. Update the comment to reflect this.

Fixes: 2ffc871a

 ('xprtrdma: Release orphaned MRs immediately')
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>