net: sfp: convert register indexes from hex to decimal

The register indexes in the standards are in decimal rather than hex,
so lets specify them in decimal in the header file so we can easily
cross-reference without converting between hex and decimal.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>