omap: McBSP: Fix incorrect receiver stop in omap_mcbsp_stop

This small typo written by author causes that McBSP receiver is disabled on
OMAP2430 and OMAP3430 even if only transmitter is stopped. This was noted
with ALSA SoC where simultaneous recording halted if playback was stopped
first.

Signed-off-by: Jarkko Nikula <jhnikula@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>