iwlwifi: allow to zero SRAM

Sending a NULL pointer to iwl_trans_write_mem allows now
to zero SRAM.

Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/iwlwifi/pcie/trans.c

@@ -815,7 +815,8 @@ static int iwl_trans_pcie_write_mem(struct iwl_trans *trans, u32 addr,
 	if (iwl_trans_grab_nic_access(trans, false)) {
 		iwl_write32(trans, HBUS_TARG_MEM_WADDR, addr);
 		for (offs = 0; offs < dwords; offs++)
-			iwl_write32(trans, HBUS_TARG_MEM_WDAT, vals[offs]);
+			iwl_write32(trans, HBUS_TARG_MEM_WDAT,
+				    vals ? vals[offs] : 0);
 		iwl_trans_release_nic_access(trans);
 	} else {
 		ret = -EBUSY;