serial_core: Remove call to driver-specific TIO[GS]RS485]

Once there is no more handlers for TIOC[GS]RS485 there is no need to
call the driver specific ioctl when the generic implementation is
missing.

Reviewed-by: Alan Cox <alan@linux.intel.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>