scsi: qla4xxx: Use correct variable in memset for clarity

scsi: qla4xxx: Use correct variable in memset for clarity

Both mbox_cmd and mbox_sts have the same size, so using sizeof(mbox_cmd)
when clearing mbox_sts did not cause any functional issue. However, it
is misleading and reduces code readability.

Update the memset() calls to use sizeof(mbox_sts) to make the intent
clear

Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Link: https://patch.msgid.link/20251021090354.1804327-1-alok.a.tiwari@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>