[PATCH] libertas: remove adapter->adhoc_grate_enabled

The variable was initialized with 0 (false). There is no code that would
ever change it, so we can use the false-patch directly.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>