net: sfp: fix sfp_bus_put() kernel documentation

The kbuild test robot found a problem with htmldocs with the recent
change to the SFP interfaces.  Fix the kernel documentation for
sfp_bus_put() which was missing an '@' before the argument name
description.

Fixes: 727b3668

 ("net: sfp: rework upstream interface")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>