sh_eth: Use async pm_runtime_put()

sh_eth: Use async pm_runtime_put()

There is no stringent need to power down the device immediately after a
register read, or after a failed open.  Relax power down handling by
replacing calls to synchronous pm_runtime_put_sync() by calls to
asynchronous pm_runtime_put().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Tested-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Link: https://patch.msgid.link/77562617360e30a47746e53e392905ea312a2f97.1756998732.git.geert+renesas@glider.be
Signed-off-by: Jakub Kicinski <kuba@kernel.org>