drm/amdgpu: fix error checking in amdgpu_read_mm_registers for soc21

Properly skip non-existent registers as well.

Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/2442
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

Author: alexdeucher

drivers/gpu/drm/amd/amdgpu/soc21.c

@@ -291,9 +291,10 @@ static int soc21_read_register(struct amdgpu_device *adev, u32 se_num,
 	*value = 0;
 	for (i = 0; i < ARRAY_SIZE(soc21_allowed_read_registers); i++) {
 		en = &soc21_allowed_read_registers[i];
-		if (adev->reg_offset[en->hwip][en->inst] &&
-		    reg_offset != (adev->reg_offset[en->hwip][en->inst][en->seg]
-				   + en->reg_offset))
+		if (!adev->reg_offset[en->hwip][en->inst])
+			continue;
+		else if (reg_offset != (adev->reg_offset[en->hwip][en->inst][en->seg]
+					+ en->reg_offset))
 			continue;
 
 		*value = soc21_get_register_value(adev,