glsl: fix sizeof(pointer) bug

Doesn't really change anything to the test though ¯\_(ツ)_/¯

CID: 1429511
Fixes: e8495646af "glsl/tests: changes to test_disk_cache_create test"
Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>

src/compiler/glsl/tests/cache_test.c

@@ -186,7 +186,7 @@ static void *
 cache_exists(struct disk_cache *cache)
 {
    uint8_t dummy_key[20];
-   char *data = "some test data";
+   char data[] = "some test data";
 
    if (!cache)
       return NULL;