tools/net/ynl: add s8, s16 to valid scalars in ynl-gen-c

Add the missing s8 and s16 scalar types to the list of recognised
scalars in ynl-gen-c.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250211120127.84858-6-donald.hunter@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>