sfp: fix sparse warning

drivers/net/phy/sfp-bus.c:298:13: warning: context imbalance in 'sfp_bus_release' - wrong count at exit

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>