glcolorconvert: Fix syntax for GLSL shaders
Shader compilation was failing on macOS:
gstglslstage.c:519:_compile_shader:<glslstage1> fragment shader compilation failed:
ERROR: 0:10: 'input_swizzle' : syntax error: Array size must appear after variable name
Co-authored-by: Matthew Waters matthew@centricular.com
This broke in !5109 (merged).