net: dsa: bcm_sf2: Initialize __be16 with a __be16 value

A __be16 variable should be initialised with a __be16 value.  So add a
htons(). In this case it is pointless, given the value being assigned
is 0xffff, but it stops sparse from warnings.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>