tools/net/ynl: remove extraneous plural from variable names

_decode_array_attr() uses variable subattrs in every branch when only
one branch decodes more than a single attribute.

Change the variable name to subattr in the branches that only decode a
single attribute so that the intent is more obvious.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250211120127.84858-2-donald.hunter@gmail.com


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