Fix a spelling boo

Marlin/G26_Mesh_Validation_Tool.cpp

    *                    'n' can be used instead if your host program does not appreciate you using 'N'.
    *
    *   O #  Ooooze      How much your nozzle will Ooooze filament while getting in position to print.  This
-   *                    is over kill, but using this parameter will let you get the very first 'cicle' perfect
+   *                    is over kill, but using this parameter will let you get the very first 'circle' perfect
    *                    so you have a trophy to peel off of the bed and hang up to show how perfectly you have your
    *                    Mesh calibrated.  If not specified, a filament length of .3mm is assumed.
    *

Marlin/ubl_G29.cpp

    *                    Mesh Validation Pattern phase.   Please note that you are populating your mesh with unverified
    *                    numbers.  You should use some scrutiny and caution.
    *
-   *   P4    Phase 4    Fine tune the Mesh. The Delta Mesh Compensation System assume the existance of
+   *   P4    Phase 4    Fine tune the Mesh. The Delta Mesh Compensation System assume the existence of
    *                    an LCD Panel. It is possible to fine tune the mesh without the use of an LCD Panel.
    *                    (More work and details on doing this later!)
    *                    The System will search for the closest Mesh Point to the nozzle. It will move the