rtl8180: silence "dubious: x | !y" sparse warning

  CHECK   drivers/net/wireless/rtl818x/rtl8180_rtl8225.c
drivers/net/wireless/rtl818x/rtl8180_rtl8225.c:53:33: warning: dubious: x | !y

The existing code is clever and works fine, but it's not worth even a
single line of Sparse warning SPAM...

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