drm/etnaviv: Use 'unsigned' type to count the number of pages

The unpin_user_pages() function takes an 'unsigned long' argument to
store the number of userspace pages, and the struct drm_gem_object::size
is a size_t type. The number of pages can not be negative, hence, use
'unsigned' variable to count the number of pages.

Reviewed-by: Christian Gmeiner <[e-mail]>
Signed-off-by: Sui Jingfeng <[e-mail]>
Signed-off-by: Lucas Stach <[e-mail]>

drivers/gpu/drm/etnaviv/etnaviv_gem.c

···
 		kfree(etnaviv_obj->sgt);
 	}
 	if (etnaviv_obj->pages) {
-		int npages = etnaviv_obj->base.size >> PAGE_SHIFT;
+		unsigned int npages = etnaviv_obj->base.size >> PAGE_SHIFT;
 
 		unpin_user_pages(etnaviv_obj->pages, npages);
 		kvfree(etnaviv_obj->pages);