drivers: serial: b91: irq_tx_ready update to check TX IRQ
drivers: serial: b91: irq_tx_ready update to check TX IRQ

Updated b91_irq_tx_ready API to check TX IRQ enabled.

Signed-off-by: Yuriy Vynnychek <a84feaeb1f754105d62c9a6971fe842c95d6cc94@telink-semi.com>

finikorg/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr