progs/glsl: Fix noise GLSL compilation error on Mac OS.

(cherry picked from commit 0d31990b47)

progs/glsl/noise.c

@@ -28,7 +28,7 @@ static const char *FragShaderText =
    "   vec4 p;\n"
    "   p.xy = gl_TexCoord[0].xy;\n"
    "   p.z = Slice;\n"
-   "   p.w = 0;\n"
+   "   p.w = 0.0;\n"
    "   vec4 n = noise4(p * scale);\n"
    "   gl_FragColor = n * Scale + Bias;\n"
    "}\n";