drm/vc4: Fix memory leak of BO array in hang state

drm/vc4: Fix memory leak of BO array in hang state

The hang state's BO array is allocated separately with kzalloc() in
vc4_save_hang_state() but never freed in vc4_free_hang_state(). Add the
missing kfree() for the BO array before freeing the hang state struct.

Fixes: 214613656b51 ("drm/vc4: Add an interface for capturing the GPU state after a hang.")
Reviewed-by: Melissa Wen <mwen@igalia.com>
Link: https://patch.msgid.link/20260330-vc4-misc-fixes-v1-2-92defc940a29@igalia.com
Signed-off-by: Maíra Canal <mcanal@igalia.com>