littlefs: translate error code when mount fails

When lfs mount fails and there is no formatting requested, the return
code must be translated to errno before being passed to the application
layer.

Additionally, only log a warning that the FS will be formatted, when the
system is not read-only.

Fixes #56378

Signed-off-by: Manuel Arguelles <manuel.arguelles@nxp.com>
2 files changed