scsi: bnx2fc: Add missing annotation for bnx2fc_abts_cleanup()

Sparse reports the following warning:

  warning: context imbalance in bnx2fc_abts_cleanup() - unexpected unlock

The root cause is the missing annotation at bnx2fc_abts_cleanup(). Add the
missing __must_hold(&tgt->tgt_lock) annotation.

Link: https://lore.kernel.org/r/20200411001933.10072-8-jbi.octave@gmail.com


Signed-off-by: Jules Irenge <jbi.octave@gmail.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>