iwlagn: Fix a bug introduced by the HUGE command removal

Since we don't have HUGE command any more, there is no point in adding 1
to the num of slots in the command queue. Doing so is buggy and might corrupt
memory.

Bug introduced by 4ce7cc2b


iwlagn: support multiple TBs per command

Cc: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>