scsi: megaraid: Fix mega_cmd_done() CMDID_INT_CMDS

When cmdid == CMDID_INT_CMDS, the 'cmds' pointer is NULL but is
dereferenced below.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 0f2bb84d2a68 ("[SCSI] megaraid: simplify internal command handling")
Signed-off-by: Danila Chernetsov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/megaraid.c

···
 		 */
 		if (cmdid == CMDID_INT_CMDS) {
 			scb = &adapter->int_scb;
+			cmd = scb->cmd;
 
 			list_del_init(&scb->list);
 			scb->state = SCB_FREE;