freedreno: Fix leak of the screen hash table.
Now we have no leaks detected on a run of a basic deqp test (dEQP-GLES2.functional.shaders.constants.const_float_assignment_3_fragment).
Now we have no leaks detected on a run of a basic deqp test (dEQP-GLES2.functional.shaders.constants.const_float_assignment_3_fragment).