TTY: hvcs, clean hvcs_open a bit

Make the code of hvcs_open a bit more readable by:
- moving all assignments out of if's
- redoing fail paths so that corresponding pieces are nearby
- we need only one of retval and rc

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>