usb-serial: use new registration API in [q-s]* drivers

This patch (as1528) modifies the following usb-serial drivers to
utilize the new usb_serial_{de}register_drivers() routines:

	qcaux, qcserial, safe_serial, siemens_mpi, sierra,
	spcp8x5, ssu100, and symbolserial.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>