cxgbe(4): Use correct priority in begin_synchronized_op.

It was always set to PCATCH because the driver tested (INTR_OK) instead
of (flags & INTR_OK). Fit a WITNESS_WARN in a single line while here.

Sponsored by: Chelsio Communications

(cherry picked from commit 04bf43505bae1bb20d315a44e977d97aed3e5733)