mesa: move variable declaration to where its used

The variable replacement was unused when building w/o
ENABLE_SHADER_CACHE. Since we can mix variable declarations and code,
move it to where its used.

Fixes: 9f8dc3bf03e "utils: build sha1/disk cache only with
Android/Autoconf"
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

(cherry picked from commit 6a5850b04a86c2287112047c6cad500136d18df5)
1 file changed