Reset the struct on set_fd

Reset the struct on set_fd

libevdev_set_fd may fail at a number of points. If it does, it errors out but does nothing
otherwise. Thus, a client may call set_fd again for the same struct but on a different fd and have
it succeed. Depending on when set_fd bailed out the first time, some fields may already be set.

Thus, reset the whole struct at set_fd time to make sure we're nulled out appropriately.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>