ARM: OMAP1: mux: add missing include

ARM: OMAP1: mux: add missing include

Fix the following build breakage in v3.4-rc2 that happens
with CONFIG_OMAP_MUX=y:

arch/arm/mach-omap1/mux.c:89:1: error: 'FUNC_MUX_CTRL_9' undeclared here (not in a function)
arch/arm/mach-omap1/mux.c:89:1: error: 'PULL_DWN_CTRL_2' undeclared here (not in a function)
arch/arm/mach-omap1/mux.c:93:1: error: 'FUNC_MUX_CTRL_C' undeclared here (not in a function)

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>