egl/dri2: fix image loaderPrivate type mixup

The first callback which uses an image's loaderPrivate data was recently added. Prior to this, dri2_create_image_khr_texture had been setting the unused loaderPrivate field on the image it creates. This caused a pointer type mixup in platform_android when it started using the new callback. Fix this by no longer unnecessarily setting loaderPrivate in dri2_create_image_khr_texture.

Closes: #4010 (closed) Fixes: a2fb87ee ("egl/android: implement image cleanup callback")