serial/sirf: fixup for changes to pin control

We changed the signature of the pin multiplexing functions to
handle any pin business, so fix up the Sirf driver to call this
new interface and rename some variables to make the semantics
understandable.

Cc: linux-serial@vger.kernel.org
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>