omap: McBSP: Drop unnecessary status/error bit clearing on reg_cacheretrieved register values

The MsBSP register cache will never have any error/status flags set, since
these flags are never written to the reg_cache. So it is kind of not
necessary to clear these flags, which are actually always 0.

In other words, clearing the status/error flags are not necessary, since the
reg_cache will never got these bits set. We can just write back the
register content from the cache as it is when clearing an error condition.

Tested on Amstrad Delta.

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