scripts: Fix header ifdef guard for gen_image_info.py
scripts: Fix header ifdef guard for gen_image_info.py

gen_image_info.py was generating invalid include guard. Properly strip
all special characters from filename to generate include guard #ifdef

Signed-off-by: Daniel DeGrasse <002dd1d4ac44ebb71088aae93501e62b784ed821@nxp.com>

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