b43: LP-PHY: Two small spec updates

The specs are beginning to support rev3 LP-PHYs - implement one of
the changes needed for rev3 support.
Also, in the new MIPS driver, the "Japan TX filter" was renamed to
"analog TX filter init" - however, calling it "init" is confusing,
so name it "set analog filter", with a comment for easier future
identification.

Signed-off-by: Gábor Stefanik <netrolller.3d@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>