omap: McBSP: Fix possible port lockout

In its current form, the omap_mcbsp_request() function can return after
irq_request() failure without any cleanups, effectively locking out the port
forever with clocks left running. Fix it.

Signed-off-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Jarkko Nikula <jhnikula@gmail.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>