toradex: Fix recursive call to checkboard

Since checkboard() is used instead of show_board_info(), in case toradex
config block is missing or malformed, checkboard is recursively called.
It prints a long list of "MISSING TORADEX CONFIG BLOCK" till the stack
is full.

Fixes: edb0ecd1 ("toradex: Use checkboard() instead of show_board_info()")
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Tested-by: Marcel Ziswiler <marcel.ziswiler@toradex.com> # Verdin iMX8M Plus
Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>
Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>