radv: fix a memleak for merged shaders on GFX9

modules[i] can be NULL for merged shaders but we have to
free the NIR code. radv_can_dump_shader_stats() already handles
if modules[i] is NULL, no need to check it twice.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
(cherry picked from commit 6e32d9e7)