drm/i915: Improve debug print in vm_fault_ttm

Print the error code returned by __i915_ttm_migrate()
for better debuggability.

v2: Fix kernel test robot warning.
v3: Fix dim checkpatch warning.

References: https://gitlab.freedesktop.org/drm/intel/-/issues/6889
Acked-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220923143730.13498-1-nirmoy.das@intel.com

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -1073,7 +1073,8 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
 		}
 
 		if (err) {
-			drm_dbg(dev, "Unable to make resource CPU accessible\n");
+			drm_dbg(dev, "Unable to make resource CPU accessible(err = %pe)\n",
+				ERR_PTR(err));
 			dma_resv_unlock(bo->base.resv);
 			ret = VM_FAULT_SIGBUS;
 			goto out_rpm;