drivers: serial: uart_cdns: fix interrupt driven for shell

[frankshuweilin]

Describe the bug
With Cadence UART (driver: uart_cdns.c) as the shell backend, if both CONFIG_UART_INTERRUPT_DRIVEN and CONFIG_SHELL_BACKEND_SERIAL_INTERRUPT_DRIVEN are enabled, the console does not response properly. You will get unexpected echos when you type in commands.

The target platform is our proprietary with Cadence UART IP in it. The Zephyr version is 3.4.0.

To Reproduce
In prj.conf file, set
CONFIG_SHELL=y
CONFIG_SHELL_BACKENDS=y
CONFIG_SHELL_BACKEND_SERIAL=y
CONFIG_SHELL_BACKEND_SERIAL_INTERRUPT_DRIVEN=y
CONFIG_CONSOLE=y
CONFIG_UART_INTERRUPT_DRIVEN=y
CONFIG_UART_CONSOLE=y

Expected behavior
When typing in commands in UART terminal, proper echos should be seen

Impact
Not able to use CONFIG_SHELL_BACKEND_SERIAL_INTERRUPT_DRIVEN=y

Logs and console output
N/A

Environment (please complete the following information):

• OS: Fedora 38
• gtkterm

[github-actions]

Hi @frankshuweilin! We appreciate you submitting your first issue for our open-source project. 🌟

Even though I'm a bot, I can assure you that the whole community is genuinely grateful for your time and effort. 🤖💙