Bluetooth: Use single return in hci_uart_tty_ioctl() call

Remove multiple return statements in hci_uart_tty_ioctl() call and
added a single return statement.

This code re-organisation allows subsequent locking to be easily
added.

Signed-off-by: Vignesh Raman <Vignesh_Raman@mentor.com>
Signed-off-by: Dean Jenkins <Dean_Jenkins@mentor.com>
Signed-off-by: Rajeev Kumar <rajeev_kumar@mentor.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>