ASoC: OMAP: fix OMAP1 compilation problem

In the new code introduced with commit cf4c87ab

,
"OMAP: McBSP: implement McBSP CLKR and FSR signal muxing via mach-omap2/mcbsp.c",
the way omap1 build is supposed to bypass omap2 specific functionality doesn't
optimize out all omap2 specific stuff. This breaks linking phase for omap1
machines, giving "undefined reference to `omap2_mcbsp1_mux_clkr_src'"
and "undefined reference to `omap2_mcbsp1_mux_fsr_src'" errors. Fix it.

Created and tested against linux-2.6.37-rc1.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Paul Walmsley <paul@pwsan.com>
Acked-by: Jarkko Nikula <jhnikula@gmail.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>