opengl/gltexture: Fix format for 565 textures
GL_INVALID_OPERATION is generated if type is one of [...] GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, [...] and format is not GL_RGB.
Found this while testing strides for !6228 (closed)
GL_INVALID_OPERATION is generated if type is one of [...] GL_UNSIGNED_SHORT_5_6_5, GL_UNSIGNED_SHORT_5_6_5_REV, [...] and format is not GL_RGB.
Found this while testing strides for !6228 (closed)