kernel: mtdsplit: rework and make use of -ENOENT error

kernel: mtdsplit: rework and make use of -ENOENT error

Rework each affected mtdsplit driver to make use of -ENOENT error
instead of -ENODEV to handle new kernel that checks error from parser on
subpartitions.

The only acceptable error is -ENOENT that skip the parser. This follow
pattern used upstream and also by an mtdsplit parser, mtdsplit_bcm_wfi,
and also by a workaround currently implemented for mtdsplit_mstc_boot.

Signed-off-by: Christian Marangi <[email protected]>