brcmsmac: update comment to reflect the code

The brcms_attach function is defined as static but the comment is
saying that it should not be static or gcc will issue a warning.
I believe we can remove the comment as I don't se a problem with
this function being defined as static.

Signed-off-by: Emil Goode <emilgoode@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>