egl/x11: Fix driver_name acquisition

egl/x11: Fix driver_name acquisition

We don't need to free driverName string from dri2 reply, on the other
hand, the driver name acquired from loader doesn't need duplication.

Fixes: 45e110bad9d (egl/x11: trust our loader over the xserver for the
drivername)

Reported-by: Timothy Arceri <t_arceri@yahoo.com.au>
Signed-off-by: Boyan Ding <boyan.j.ding@gmail.com>
[Emil Velikov: use brackets for both branches of conditional]
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>