openprom: Squelch useless GCC warning.

drivers/sbus/char/openprom.c: In function ‘openprom_sunos_ioctl’:
drivers/sbus/char/openprom.c:306: warning: ‘opp’ may be used uninitialized in this function

Signed-off-by: David S. Miller <davem@davemloft.net>