helper/command: fix echo return values

helper/command: fix echo return values

the echo command is managed through command handler and not jim_handler
to be consistent rename the handler from jim_echo to handle_echo
and update the return values

Fixes: 4747af362de0 (JIM: document "echo" command)
Change-Id: I5ae87ea802d8430b573fb83daa6b35490b5d5775
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6549
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>