drm/amdgpu: Fix wait for RLCG command completion

if (!(tmp & flag)) condition will always evaluate to true
when the flag is 0x0 (AMDGPU_RLCG_GC_WRITE). Instead check
that address bits are cleared to determine whether
the command is complete.

Signed-off-by: Victor Skvortsov <victor.skvortsov@amd.com>
Tested-by: Bokun Zhang <bokun.zhang@amd.com>
Reviewed by: Shaoyun.liu <Shaoyun.liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>