ssb: PCI revision ID register is 8-bit wide

The SSB code reads PCI revision ID register as 16-bit entity while the register
is actually 8-bit only (the next 8 bits are the programming interface register).
Fix the read and make the 'rev' field of 'struct ssb_boardinfo' 8-bit as well,
to match the register size.

Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>