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>