Propogate the init/shutdown mutex through the setserial logic. Use the proper
locks for the various bits still using the BKL. Kill the BKL in this driver.

Updated to fix the bug noted by Dan Carpenter
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>