drm/etnaviv: clean up etnaviv_gem_new_handle

Setting the GFP flags does not need a new code block if moved to
the right location, which makes this function a bit easier to read.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>