mwl8k: pci BAR mapping changes

Map BAR0 as well, as we need to write to it during init on some chips.

Also, if BAR0 is a 64bit BAR, the register BAR becomes BAR2, so try
mapping BAR2 if mapping BAR1 fails.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>