gldownloadelement: fix export of odd width textures

New GPU driver changed the default stride calculations when resolving
textures to external surfaces. To get tightly packed RGB out of i.MX8MQ we
now must specify the stride value explicitly.

BUG: 157921487
Change-Id: I0ef6bf1cfc3230ff8a4097e6db0766f04a100f53
1 file changed