ARM: imx35 Bugfix admux clock

The admux clock seems to be the audmux clock as tests show. audmux does
not work without this clock enabled. Currently imx35 does not register a
clock device for audmux. This patch adds this registration. imx-audmux
driver already handles a clock device, so no changes are necessary
there.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>