scsi: myrs: Fix crash in error case

In myrs_detect(), cs->disable_intr is NULL when privdata->hw_init() fails
with non-zero. In this case, myrs_cleanup(cs) will call a NULL ptr and
crash the kernel.

[    1.105606] myrs 0000:00:03.0: Unknown Initialization Error 5A
[    1.105872] myrs 0000:00:03.0: Failed to initialize Controller
[    1.106082] BUG: kernel NULL pointer dereference, address: 0000000000000000
[    1.110774] Call Trace:
[    1.110950]  myrs_cleanup+0xe4/0x150 [myrs]
[    1.111135]  myrs_probe.cold+0x91/0x56a [myrs]
[    1.111302]  ? DAC960_GEM_intr_handler+0x1f0/0x1f0 [myrs]
[    1.111500]  local_pci_probe+0x48/0x90

Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Hannes Reinecke <[email protected]>
Signed-off-by: Tong Zhang <[email protected]>
Signed-off-by: Martin K. Petersen <[email protected]>

Author: lzto

drivers/scsi/myrs.c

@@ -2267,7 +2267,8 @@ static void myrs_cleanup(struct myrs_hba *cs)
 	myrs_unmap(cs);
 
 	if (cs->mmio_base) {
-		cs->disable_intr(cs);
+		if (cs->disable_intr)
+			cs->disable_intr(cs);
 		iounmap(cs->mmio_base);
 		cs->mmio_base = NULL;
 	}