staging: pi433: Move limit check to switch default to kill warning

With gcc-4.1.2:

drivers/staging/pi433/rf69.c: In function ‘rf69_set_dio_mapping’:
drivers/staging/pi433/rf69.c:566: warning: ‘regaddr’ may be used uninitialized in this function
drivers/staging/pi433/rf69.c:565: warning: ‘shift’ may be used uninitialized in this function
drivers/staging/pi433/rf69.c:564: warning: ‘mask’ may be used uninitialized in this function

While this is a false positive, it can easily be fixed by moving the
limit check into the "default" case of the switch statement.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/pi433/rf69.c

···
 		dev_dbg(&spi->dev, "set: DIO mapping");
 	#endif
 
-	// check DIO number
-	if (DIONumber > 5) {
-		dev_dbg(&spi->dev, "set: illegal input param");
-		return -EINVAL;
-	}
-
 	switch (DIONumber) {
 	case 0: mask=MASK_DIO0; shift=SHIFT_DIO0; regaddr=REG_DIOMAPPING1; break;
 	case 1: mask=MASK_DIO1; shift=SHIFT_DIO1; regaddr=REG_DIOMAPPING1; break;
···
 	case 3: mask=MASK_DIO3; shift=SHIFT_DIO3; regaddr=REG_DIOMAPPING1; break;
 	case 4: mask=MASK_DIO4; shift=SHIFT_DIO4; regaddr=REG_DIOMAPPING2; break;
 	case 5: mask=MASK_DIO5; shift=SHIFT_DIO5; regaddr=REG_DIOMAPPING2; break;
+	default:
+		dev_dbg(&spi->dev, "set: illegal input param");
+		return -EINVAL;
 	}
 
 	// read reg