kbuild: uapi: upgrade check_sizetypes() warning to error

No problematic type usages exist anymore.

Make sure it stays this way.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Link: https://lore.kernel.org/r/20250813-kbuild-hdrtest-fixes-v2-4-8a7921ca3a03@linutronix.de
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

Author: t-8ch

usr/include/headers_check.pl

@@ -159,7 +159,6 @@ sub check_sizetypes
 		              "found __[us]{8,16,32,64} type " .
 		              "without #include <linux/types.h>\n";
 		$linux_types = 2;
-		# Warn until headers are all fixed
-		#$ret = 1;
+		$ret = 1;
 	}
 }