bluetooth: classic: Fix remote name resolving with multiple devices

The error occur when discoverying br devices and need to send request_name
for many found devices.
In system work queue task, bt_hci_inquiry_complete->
report_discovery_results is called, then request_name is called for all
the found devices. The controller gives HCI_Remote_Name_Request_Complete
event for every name request result and one buf is allocated from
hci_rx_pool to save HCI_Remote_Name_Request_Complete. When system work
queue task is blocked to call request_name for every device, many
HCI_Remote_Name_Request_Complete are received for the already sent
request_name, it uses up all the buf of hci_rx_pool, then the bt_rx_thread
task is blocked to get buf from hci_rx_pool when next
HCI_Remote_Name_Request_Complete is received, meanwhile the next
request_name send hci cmd and wait the result, but the hci status/complete
event can't be received because the bt_rx_thread is blocked and
bt_uart_isr is kept in the state to receive last
HCI_Remote_Name_Request_Complete, then bt_dev.ncmd_sem is not released,
then the next request_name send hci cmd again, but the bt_dev.ncmd_sem is
invalid, then bt_hci_cmd_send_sync fail and assert.

resolve it by requesting name one by one.

Signed-off-by: Mark Wang <yichang.wang@nxp.com>