iwlwifi: pcie: clean up ICT allocation code

Since iwl_trans_pcie_alloc_ict is called in the PCIe
allocation code, we always set CSR_INT_BIT_RX_PERIODIC.
Move that bit to the default list of interrupts we enable
and simplify the code.
Also use dma_zalloc_ and avoid to memset the memory
afterwards.
trans_pcie->ict_index is 0 since trans_pcie has just been
kzalloced, remove the redundant assignment.

Reviewed-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
diff --git a/drivers/net/wireless/iwlwifi/iwl-csr.h b/drivers/net/wireless/iwlwifi/iwl-csr.h
index da4eca8..bbab26e 100644
--- a/drivers/net/wireless/iwlwifi/iwl-csr.h
+++ b/drivers/net/wireless/iwlwifi/iwl-csr.h
@@ -198,7 +198,8 @@
 				 CSR_INT_BIT_RF_KILL | \
 				 CSR_INT_BIT_SW_RX   | \
 				 CSR_INT_BIT_WAKEUP  | \
-				 CSR_INT_BIT_ALIVE)
+				 CSR_INT_BIT_ALIVE   | \
+				 CSR_INT_BIT_RX_PERIODIC)
 
 /* interrupt flags in FH (flow handler) (PCI busmaster DMA) */
 #define CSR_FH_INT_BIT_ERR       (1 << 31) /* Error */