mount: improve handling mounts table size

This is static array with a size set to MAX_MOUNTED. Old code:
1) Was never using the last table entry/row
2) Was logging the same message for every mount entry above limit

This fixes off-by-one, moves limit check to the proper place and uses
"break" when needed.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>