drm/amdgpu: Fix warnings in gfxhub_v2_1.c

Fix the below checkpatch warnings:

WARNING: static const char * array should probably be static const char * const
+static const char *gfxhub_client_ids[] = {

WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
+       unsigned i;

WARNING: Missing a blank line after declarations
+       int i;
+       adev->gmc.VM_L2_CNTL = RREG32_SOC15(GC, 0, mmGCVM_L2_CNTL);

WARNING: Missing a blank line after declarations
+       int i;
+       WREG32_SOC15(GC, 0, mmGCVM_L2_CNTL, adev->gmc.VM_L2_CNTL);

WARNING: braces {} are not necessary for single statement blocks
+       if (!time) {
+               DRM_WARN("failed to wait for GRBM(EA) idle\n");
+       }

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>