freedreno/drm: Fix memory leak in softpin implementation

freedreno/drm: Fix memory leak in softpin implementation

Free the memory allocated for cmds/reloc_bos array when destoying the
associated ringbuffer.

For similar fix for the non-softpin implementation see:
https://gitlab.freedesktop.org/mesa/mesa/commit/d014af98b7afc69f4f733c8b8b6f2e3438e68407

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2324
Fixes: f3cc0d2 ("freedreno: import libdrm_freedreno + redesign submit")
Signed-off-by: Lasse Lopperi <lasse.lopperi@ge.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3342>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3342>