cogl-texture-2d: Regenerate the mipmaps when the texture is modified
cogl-texture-2d: Regenerate the mipmaps when the texture is modified

When the texture is modified by cogl_texture_set_region, it wasn't
setting mipmaps_dirty so it would never update the mipmaps.

Distrotech/cogl,spatulasnout/cogl,djdeath/cogl,gcampax/cogl,spatulasnout/cogl,djdeath/cogl-android,gcampax/cogl,djdeath/cogl-android,djdeath/cogl,Distrotech/cogl,Distrotech/cogl,gcampax/cogl,collects/cogl,djdeath/cogl-android,djdeath/cogl,collects/cogl,gcampax/cogl,Distrotech/cogl