iwlwifi: mvm: fix possible division by zero

Theoretically we may get only one IRQ from OS, in which
case we will have only 1 queue even in MSIx mode.
This will cause division by zero in the indirection table
calculation.
We do not need send the command in that case, as there is
only one queue so all RX traffic will be directed to it
anyway. Bail out early if there is only one queue.

Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>