net: ethernet: fs_enet: Make the per clock optional

net: ethernet: fs_enet: Make the per clock optional

Some platforms that use fs_enet don't have the PER register clock. This
optional dependency on the clock was incorrectly made mandatory when
switching to devm_ accessors.

Reported-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Closes: https://lore.kernel.org/netdev/4e4defa9-ef2f-4ff1-95ca-6627c24db20c@wanadoo.fr/
Fixes: c614acf6e8e1 ("net: ethernet: fs_enet: simplify clock handling with devm accessors")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/20240914081821.209130-1-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>