drm/amdgpu: fix error checking in amdgpu_read_mm_registers for soc15

Properly skip non-existent registers as well.

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

Author: alexdeucher

drivers/gpu/drm/amd/amdgpu/soc15.c

@@ -439,8 +439,9 @@ static int soc15_read_register(struct amdgpu_device *adev, u32 se_num,
 	*value = 0;
 	for (i = 0; i < ARRAY_SIZE(soc15_allowed_read_registers); i++) {
 		en = &soc15_allowed_read_registers[i];
-		if (adev->reg_offset[en->hwip][en->inst] &&
-			reg_offset != (adev->reg_offset[en->hwip][en->inst][en->seg]
+		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;