media: mediatek: vcodec: Fix oops when HEVC init fails

media: mediatek: vcodec: Fix oops when HEVC init fails

The stateless HEVC decoder saves the instance pointer in the context
regardless if the initialization worked or not. This caused a use after
free, when the pointer is freed in case of a failure in the deinit
function.
Only store the instance pointer when the initialization was successful,
to solve this issue.

 Hardware name: Acer Tomato (rev3 - 4) board (DT)
 pstate: 80400009 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : vcodec_vpu_send_msg+0x4c/0x190 [mtk_vcodec_dec]
 lr : vcodec_send_ap_ipi+0x78/0x170 [mtk_vcodec_dec]
 sp : ffff80008750bc20
 x29: ffff80008750bc20 x28: ffff1299f6d70000 x27: 0000000000000000
 x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
 x23: ffff80008750bc98 x22: 000000000000a003 x21: ffffd45c4cfae000
 x20: 0000000000000010 x19: ffff1299fd668310 x18: 000000000000001a
 x17: 000000040044ffff x16: ffffd45cb15dc648 x15: 0000000000000000
 x14: ffff1299c08da1c0 x13: ffffd45cb1f87a10 x12: ffffd45cb2f5fe80
 x11: 0000000000000001 x10: 0000000000001b30 x9 : ffffd45c4d12b488
 x8 : 1fffe25339380d81 x7 : 0000000000000001 x6 : ffff1299c9c06c00
 x5 : 0000000000000132 x4 : 0000000000000000 x3 : 0000000000000000
 x2 : 0000000000000010 x1 : ffff80008750bc98 x0 : 0000000000000000
 Call trace:
  vcodec_vpu_send_msg+0x4c/0x190 [mtk_vcodec_dec]
  vcodec_send_ap_ipi+0x78/0x170 [mtk_vcodec_dec]
  vpu_dec_deinit+0x1c/0x30 [mtk_vcodec_dec]
  vdec_hevc_slice_deinit+0x30/0x98 [mtk_vcodec_dec]
  vdec_if_deinit+0x38/0x68 [mtk_vcodec_dec]
  mtk_vcodec_dec_release+0x20/0x40 [mtk_vcodec_dec]
  fops_vcodec_release+0x64/0x118 [mtk_vcodec_dec]
  v4l2_release+0x7c/0x100
  __fput+0x80/0x2d8
  __fput_sync+0x58/0x70
  __arm64_sys_close+0x40/0x90
  invoke_syscall+0x50/0x128
  el0_svc_common.constprop.0+0x48/0xf0
  do_el0_svc+0x24/0x38
  el0_svc+0x38/0xd8
  el0t_64_sync_handler+0xc0/0xc8
  el0t_64_sync+0x1a8/0x1b0
 Code: d503201f f9401660 b900127f b900227f (f9400400)

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Fixes: 2674486aac7d ("media: mediatek: vcodec: support stateless hevc decoder")
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>