ssb: remove 5GHz antenna gain from sprom

There is no 2.4 GHz or 5GHz antenna gain stored in sprom. The sprom
just stores the gain values for antenna 1 and 2 or 1 to 4 for more
recent sprom versions. On old devices antenna 2 was used for 5 GHz wifi.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>