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.