rtl818x_pci: Fix BSSID register written incorrectly

rtl818x_pci: Fix BSSID register written incorrectly

BSSID register was written with six byte-writes.
It seems that, similarly to what happens with MAC registers, they needs to be
written with one 16-bit and one 32-bit writes, otherwise the write does not work.

The byte write didn't work only on my rtl8185, while it worked on rtl8180 and
rtl8187se, BTW since there are probably a number of different ASIC revisions out
of there, I let the change to affect all cards.
It shouldn't hurt anyway.

Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>