iwlwifi: pcie: fix the set of DMA memory mask

Our 9000 device supports 64 bit DMA address for RX only, and
not for TX.
Setting DMA mask to 64 for the whole device is erroneous - we
can do it only for a000 devices where device is capable of
both RX & TX DMA with 64 bit address space.

Fixes: 96a6497b ("iwlwifi: pcie: add 9000 series multi queue rx DMA support")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>