Update drivers/amlogic/hdmi/hdmi_tx/hdmi_cec_key.c

[cec] Map the "Exit" key to BACK_SPACE (Up one level in XBMC) instead of escape (Return to the home screen in XBMC).
Merge pull request #3 from jajoflo/cec_back_key_fix

[cec] Map the "Exit" key to BACK_SPACE