p54: fix "‘ret’ may be used uninitialized" warning

drivers/net/wireless/p54/p54common.c: In function ‘p54_config’:
drivers/net/wireless/p54/p54common.c:1853: warning: ‘ret’ may be used uninitialized in this function

Signed-off-by: John W. Linville <linville@tuxdriver.com>