tty: serial: linflexuart: Fix to check return value of platform_get_irq() in linflex_probe()

The platform_get_irq might be failed and return a negative result. So
there should have an error handling code.

Fixed this by adding an error handling code.

Signed-off-by: Zhang Shurong <zhang_shurong@foxmail.com>
Link: https://lore.kernel.org/r/tencent_234B0AACD06350E10D7548C2E086A9166305@qq.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>