sfp: fix RX_LOS signal handling

The options word is a be16 quantity, so we need to test the flags
having converted the endian-ness.  Convert the flag bits to be16,
which can be optimised by the compiler, rather than converting a
variable at runtime.

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