[PATCH] libertas: remove adapter->multipledtim

multipledtim was initialized with MRVDRV_DEFAULT_MULTIPLE_DTIM and then
kept at that value, so we could use that define directly.

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