coredump: adjust mem_region find in gdbstub
coredump: adjust mem_region find in gdbstub

Adjust get_mem_region to not return region when address == end
as there will be nothing to read there. Also, a subsequent region
may have that address as a start address and would be a more appropriate
selection.

Signed-off-by: Mark Holden <331a2a75f19676c53de9b901ff95cfec22b03721@fb.com>

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