brcmsmac: fix brcms_c_country_valid()

ccode is not NUL terminated.  Presumably insisting on a terminator makes
brcms_c_country_valid() return false when it's not intended.  ccode[2]
is sprom->leddc_on_time.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>