samples: usb: Exclude frdm_kl25z from USB DFU test
samples: usb: Exclude frdm_kl25z from USB DFU test

Flash is disabled on frdm_kl25z

Signed-off-by: Mahesh Mahadevan <7f315ec3481825d543f8bec256ad86a4adc9dd8a@nxp.com>

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