spirv2dxil: Fix memory leak on error path.

Fix resource leak reported by Coverity Scan.

Resource leak (RESOURCE_LEAK)
leaked_storage: Variable file_contents going out of scope leaks the storage it points to.

Fixes: 531d17c334 ("spirv2dxil: Support linking multiple shaders")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20576>

src/microsoft/spirv_to_dxil/spirv2dxil.c

@@ -92,6 +92,7 @@ compile_shader(const char *filename, gl_shader_stage shader_stage, struct shader
    if (file_size % WORD_SIZE != 0) {
       fprintf(stderr, "%s size == %zu is not a multiple of %d\n", filename,
               file_size, WORD_SIZE);
+      free(file_contents);
       return false;
    }