gl-renderer: fix texcoord in shader desc
Seems like a typo, found by reading shader debug scope logs and wondering why "!?!?" is there, e.g.:
Deleting shader program for: !?!? SHADER_VARIANT_XYUV SHADER_COLOR_CURVE_IDENTITY SHADER_COLOR_MAPPING_IDENTITY SHADER_COLOR_CURVE_IDENTITY -input_is_premult -green
cc @molinari