drm/i915/dram: return -EINVAL instead of -1

Avoid using the incidental -EPERM.
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/e2f79220ed2558f615c051e2533275a5dae1a04f.1633000838.git.jani.nikula@intel.com

drivers/gpu/drm/i915/intel_dram.c

@@ -444,7 +444,7 @@ static int icl_pcode_read_mem_global_info(struct drm_i915_private *dev_priv)
 			break;
 		default:
 			MISSING_CASE(val & 0xf);
-			return -1;
+			return -EINVAL;
 		}
 	} else {
 		switch (val & 0xf) {
@@ -462,7 +462,7 @@ static int icl_pcode_read_mem_global_info(struct drm_i915_private *dev_priv)
 			break;
 		default:
 			MISSING_CASE(val & 0xf);
-			return -1;
+			return -EINVAL;
 		}
 	}