net: sfp: use hwmon_sanitize_name()

Instead of open-coding the bad characters replacement in the hwmon name,
use the new hwmon_sanitize_name().

Signed-off-by: Michael Walle <michael@walle.cc>
Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>