parport: dead code in pp_write

We always update bytes_written before we check signal_pending so it
follows that we can't get a signal return for 0 bytes so we don't
need to check in the singal path. The cases a signal causes an earlier
abort are handled before this and will not hit this path

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>