scsi: qla2xxx: Avoid req_q_map double-read in qla2x00_error_entry()

In the Linux kernel, the following vulnerability has been resolved: scsi: qla2xxx: Avoid req_q_map double-read in qla2x00_error_entry() qla2x00_error_entry() reads ha->req_q_map[que] twice: once for the NULL check and again when assigning it to req. The map slot is cleared by qla25xx_free_req_que() (ha->req_q_map[que_id] = NULL under mq_lock) during queue teardown, while the response-queue interrupt that drives qla2x00_error_entry() is still registered (the IRQ is released later in qla25xx_free_rsp_que()). If the slot is set to NULL between the two reads, req becomes NULL and is dereferenced. Read the slot once into req and NULL-check the local before use. mq_lock is a mutex and cannot be taken from interrupt context, so the single read plus local check is the appropriate fix for the reported NULL dereference.