net: sfp: rename sm_retries

Rename sm_retries as sm_fault_retries, as this is what this member is
tracking.

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>