drivers: modem: gsm: Fix to COPS cmd parse info
drivers: modem: gsm: Fix to COPS cmd parse info

drivers: modem: gsm: Quectel EC21 and BG9x act as a gsm modem without
problem, but COPS commands can returns just one value with 'mode'.

Format and oper are not mandatory. This modification reads 'mode'.
Also a modification on modem_cmd_read_cops_cmd is needed.

Signed-off-by: Jair Jack <596727c8a0ea4db3ba2ceceedccbacd3d7b371b8@icatorze.com.br>

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