drm/i915/gt: Pass the -EINVAL when emit_pte doesn't update any PTE

When emit_pte doesn't update any PTE with return value as 0, interpret
it as -EINVAL.

v2:
  Add missing goto [Thomas]
Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405150840.29351-5-ramalingam.c@intel.com

drivers/gpu/drm/i915/gt/intel_migrate.c

@@ -577,7 +577,11 @@ intel_context_migrate_copy(struct intel_context *ce,
 
 		len = emit_pte(rq, &it_src, src_cache_level, src_is_lmem,
 			       src_offset, CHUNK_SZ);
-		if (len <= 0) {
+		if (!len) {
+			err = -EINVAL;
+			goto out_rq;
+		}
+		if (len < 0) {
 			err = len;
 			goto out_rq;
 		}