Fix floppy driver lock-up when you have an irq storm.

It happens with misconfigured interrupts (and no floppy
controller).

We should probably also make floppy use the irq probing
mechanism, which handles that situation more gracefully.

drivers/block/floppy.c

@@ -1787,10 +1787,11 @@ irqreturn_t floppy_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 		} while ((ST0 & 0x83) != UNIT(current_drive) && inr == 2
 			 && max_sensei);
 	}
-	if (handler)
-		schedule_bh(handler);
-	else
+	if (!handler) {
 		FDCS->reset = 1;
+		return IRQ_NONE;
+	}
+	schedule_bh(handler);
 	is_alive("normal interrupt end");
 
 	/* FIXME! Was it really for us? */