isdn: mISDNinfineon: fix potential NULL pointer dereference

In case ioremap fails, the fix returns -ENOMEM to avoid NULL
pointer dereference.
Signed-off-by: NKangjie Lu <kjlu@umn.edu>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/isdn/hardware/mISDN/mISDNinfineon.c

@@ -712,8 +712,11 @@ setup_io(struct inf_hw *hw)
 				(ulong)hw->addr.start, (ulong)hw->addr.size);
 			return err;
 		}
-		if (hw->ci->addr_mode == AM_MEMIO)
+		if (hw->ci->addr_mode == AM_MEMIO) {
 			hw->addr.p = ioremap(hw->addr.start, hw->addr.size);
+			if (unlikely(!hw->addr.p))
+				return -ENOMEM;
+		}
 		hw->addr.mode = hw->ci->addr_mode;
 		if (debug & DEBUG_HW)
 			pr_notice("%s: IO addr %lx (%lu bytes) mode%d\n",