net: sfp: return the number of written bytes for smbus single byte access

net: sfp: return the number of written bytes for smbus single byte access

[ Upstream commit 13ff3e724207f579d3c814ee05516fefcb4f32e8 ]

We expect the SFP write accessors to return the number of written bytes.
We fail to do so for single-byte smbus accesses, which may cause errors
when setting a module's high-power state and for some cotsworks modules.

Let's return the amount of written bytes, as expected.

Fixes: 7662abf4db94 ("net: phy: sfp: Add support for SMBus module access")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20260105151840.144552-1-maxime.chevallier@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>