b43: extract one more radio parameter: version

Some radios may share the same ID and revision but differ by a version.
E.g. radio in BCM5357B0 is version 1 and requires specific handling.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>