drm/etnaviv: Drop the second argument of the etnaviv_gem_new_impl()

The mentioned second parameter is the 'u32 size', but it is not get used by
the etnaviv_gem_new_impl() function, so drop it. No functional change.

Signed-off-by: Sui Jingfeng <suijingfeng@loongson.cn>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>