ext4: add new trace event in ext4_fc_cleanup

This adds a new trace event in ext4_fc_cleanup() which is helpful in debugging
some fast_commit issues.

Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/794cdb1d5d3622f3f80d30c222ff6652ea68c375.1647057583.git.riteshh@linux.ibm.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>