scsi: qla2xxx: Format log strings only if needed

Commit 598a90f2 ("scsi: qla2xxx: add ring buffer for tracing debug
logs") introduced unconditional log string formatting to ql_dbg() even if
ql_dbg_log event is disabled. It harms performance because some strings are
formatted in fastpath and/or interrupt context.

Link: https://lore.kernel.org/r/20211112145446.51210-1-r.bolshakov@yadro.com
Fixes: 598a90f2

 ("scsi: qla2xxx: add ring buffer for tracing debug logs")
Cc: Rajan Shanmugavelu <rajan.shanmugavelu@oracle.com>
Cc: stable@vger.kernel.org
Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>