net: dsa: mv88e6xxx: Add missing static to stub functions

'static' was not enough, the helpers must be 'static inline'

net/dsa/mv88e6xxx/global2.h:123:12: error: 'mv88e6xxx_g2_misc_4_bit_port' defined but not used [-Werror=unused-function]
net/dsa/mv88e6xxx/global2.h:117:12: error: 'mv88e6xxx_g2_pvt_write' defined but not used [-Werror=unused-function]

Fixes: c21fbe29 ("net: dsa: mv88e6xxx: Add missing static to stub functions")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>