ARM: lib/lib1funcs.S: fix typo s/substractions/subtractions/

Signed-off-by: Antonio Ospite <ao2@ao2.it>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Christoffer Dall <christoffer.dall@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>