drm/amdgpu: Fix with right return code '-EIO' in 'amdgpu_gmc_vram_checking()'

The amdgpu_gmc_vram_checking() function in emulation checks whether
all of the memory range of shared system memory could be accessed by
GPU, from this aspect, -EIO is returned for error scenarios.

Fixes the below:
drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c:919 gmc_v6_0_hw_init() warn: missing error code? 'r'
drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c:1103 gmc_v7_0_hw_init() warn: missing error code? 'r'
drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c:1223 gmc_v8_0_hw_init() warn: missing error code? 'r'
drivers/gpu/drm/amd/amdgpu/gmc_v9_0.c:2344 gmc_v9_0_hw_init() warn: missing error code? 'r'

Cc: Xiaojian Du <Xiaojian.Du@amd.com>
Cc: Lijo Lazar <lijo.lazar@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Suggested-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -1045,21 +1045,28 @@ int amdgpu_gmc_vram_checking(struct amdgpu_device *adev)
 	 * seconds, so here, we just pick up three parts for emulation.
 	 */
 	ret = memcmp(vram_ptr, cptr, 10);
-	if (ret)
-		return ret;
+	if (ret) {
+		ret = -EIO;
+		goto release_buffer;
+	}
 
 	ret = memcmp(vram_ptr + (size / 2), cptr, 10);
-	if (ret)
-		return ret;
+	if (ret) {
+		ret = -EIO;
+		goto release_buffer;
+	}
 
 	ret = memcmp(vram_ptr + size - 10, cptr, 10);
-	if (ret)
-		return ret;
+	if (ret) {
+		ret = -EIO;
+		goto release_buffer;
+	}
 
+release_buffer:
 	amdgpu_bo_free_kernel(&vram_bo, &vram_gpu,
 			&vram_ptr);
 
-	return 0;
+	return ret;
 }
 
 static ssize_t current_memory_partition_show(