net: sfp: clean up i2c-bus property parsing

We currently have some complicated code in sfp_probe() which gets the
I2C bus depending on whether the sfp node is DT or ACPI, and we use
completely separate lookup functions.

This could do with being in a separate function to make the code more
readable, so move it to a new function, sfp_i2c_get(). We can also use
fwnode_find_reference() to lookup the I2C bus fwnode before then
decending into fwnode-type specific parsing.

A future cleanup would be to move the fwnode-type specific parsing into
the i2c layer, which is where it really should be.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://lore.kernel.org/r/E1p1WGJ-0098wS-4w@rmk-PC.armlinux.org.uk


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