mgba seems not work with gbc rom
maybe you can try to create a new menu item with this action.config in ssh
ROM=/home/cpi/games/MGBA
ROM_SO=/home/cpi/apps/emulators/gambatte_libretro.so
EXT=gb,gbc
LAUNCHER=retroarch -L
TITLE=GBC Roms
SO_URL=http://buildbot.libretro.com/nightly/linux/armv7-neon-hf/latest/gambatte_libretro.so.zip
mkdir ~/apps/Menu/20_Retro\ Games/31_GBC