tools: ynl: don't skip regeneration from make targets

tools: ynl: don't skip regeneration from make targets

Commit 2b7ac0c87d98 ("tools: ynl-gen: don't touch the output file if
content is the same") is working too well. It was added so that
ynl-regen -f doesn't make us rebuild half of the kernel, if there
are no actual changes in any generated code.

When ynl-gen-c is called by make, however, we're better off trusting
make's tracking and overwrite the file. Otherwise if output is identical
we won't update file timestamps and make will retry code gen on every
invocation.

Link: https://lore.kernel.org/r/20231129193622.2912353-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>