Bluetooth: hci_qca: Add delay for wcn3990 stability

On the msm8998 mtp, the response to the baudrate change command is never
received.  On the Lenovo Miix 630, the response to the baudrate change
command is corrupted - "Frame reassembly failed (-84)".

Adding a 50ms delay before re-enabling flow to receive the baudrate change
command response from the wcn3990 addesses both issues, and allows
bluetooth to become functional.

Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>