drm/amdgpu: Fix warnings in gfxhub_v2_0.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
+       u32 tmp;
+       tmp = RREG32_SOC15(GC, 0, mmGCVM_L2_PROTECTION_FAULT_CNTL);

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>