configs: omapl138_lcdk: decrease the loglevel to reduce the size of the SPL

The changes in the MMC stack have increased its footprint up to the point
were its breaks the generation of the SPL for this platform.
Fix this by reducing the loglevel.

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Peter Howard <phoward@gme.net.au>