selftests: harness: Remove inline qualifier for wrappers

The pointers to the wrappers are stored in function pointers,
preventing them from actually being inlined.
Remove the inline qualifier, aligning these wrappers with the other
functions defined through macros.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250505-nolibc-kselftest-harness-v4-5-ee4dd5257135@linutronix.de


Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>