Spelling: It's Versus Its

Corrects incorrect usage of contraction for 'it is', when possessive 'its' was required.

Differential Revision: https://developer.blender.org/D9250

Reviewed by Campbell Barton

source/blender/draw/engines/eevee/shaders/raytrace_lib.glsl

@@ -140,7 +140,7 @@ void prepare_raycast(vec3 ray_origin,
 
 // #define GROUPED_FETCHES /* is still slower, need to see where is the bottleneck. */
 /* Return the hit position, and negate the z component (making it positive) if not hit occurred. */
-/* __ray_dir__ is the ray direction premultiplied by it's maximum length */
+/* __ray_dir__ is the ray direction premultiplied by its maximum length */
 vec3 raycast(int index,
              vec3 ray_origin,
              vec3 ray_dir,