drm/amdgpu: Clean up errors in amdgpu_gmc.c

Fix the following errors reported by checkpatch:

ERROR: need consistent spacing around '-' (ctx:WxV)
Signed-off-by: chenxuebing <chenxb_99091@126.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -52,7 +52,7 @@ int amdgpu_gmc_pdb0_alloc(struct amdgpu_device *adev)
 	struct amdgpu_bo_param bp;
 	u64 vram_size = adev->gmc.xgmi.node_segment_size * adev->gmc.xgmi.num_physical_nodes;
 	uint32_t pde0_page_shift = adev->gmc.vmid0_page_table_block_size + 21;
-	uint32_t npdes = (vram_size + (1ULL << pde0_page_shift) -1) >> pde0_page_shift;
+	uint32_t npdes = (vram_size + (1ULL << pde0_page_shift) - 1) >> pde0_page_shift;
 
 	memset(&bp, 0, sizeof(bp));
 	bp.size = PAGE_ALIGN((npdes + 1) * 8);