wl12xx: fix warning due to missing arg in ampdu_action

Commit 0b01f030 added a new argument
to the ampdu_action operation.  The ampdu_action operation in the
wl12xx driver currently doesn't have that argument and this generates
a warning.  This happened during merging of the latest mac80211
patches with the wl12xx BA patches.

  CC [M]  drivers/net/wireless/wl12xx/main.o
drivers/net/wireless/wl12xx/main.c:3035: warning: initialization from incompatible pointer type

The wl12xx driver doesn't need to do anything about the buf_size
argument since the AMPDU TX is fully handled by the firmware.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>