drm/amd/vcn: fix an error msg on vcn 3.0

Some video card has more than one vcn instance, passing 0 to
vcn_v3_0_pause_dpg_mode is incorrect.

Error msg:
Register(1) [mmUVD_POWER_STATUS] failed to reach value
0x00000001 != 0x00000002

Reviewed-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: tiancyin <tianci.yin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org