iwlwifi: mvm: synchronize firmware DMA paging memory

When driver needs to access the contents of a streaming DMA buffer
without unmapping it it should call dma_sync_single_for_cpu().
Once the call has been made, the CPU "owns" the DMA buffer and can
work with it as needed.
Before the device accesses the buffer, however, ownership should be
transferred back to it with dma_sync_single_for_device().
Both calls weren't performed by the driver, resulting with odd paging
errors on some platforms. Fix it.

Fixes: a6c4fb44 ("iwlwifi: mvm: Add FW paging mechanism for the UMAC on PCI")
Signed-off-by: Sara Sharon <sara.sharon@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>