drm/amdgpu/vcn4: Avoid overflow on msg bound check

drm/amdgpu/vcn4: Avoid overflow on msg bound check

commit 65bce27ea6192320448c30267ffc17ffa094e713 upstream.

As pointed out by SDL, the previous condition may be vulnerable to
overflow.

Fixes: 0a78f2bac142 ("drm/amdgpu/vcn4: Prevent OOB reads when parsing dec msg")
Cc: SDL <sdl@nppct.ru>
Signed-off-by: Benjamin Cheng <benjamin.cheng@amd.com>
Reviewed-by: Ruijing Dong <ruijing.dong@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 3c5367d950140d4ec7af830b2268a5a6fdaa3885)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>