ubi-utils: Return error code if command line option is unknown

ubi-utils: Return error code if command line option is unknown

The tools in question will quit with an exit code 0 if the command
line option was not recognized. By returning an error code a calling
script has the possibility to distinguish between a real success and
an invalid invocation.

We need to return -1 instead of EXIT_FAILURE to be consistent with the
other exit code places.

Signed-off-by: Daniel Wagner <daniel.wagner@siemens.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>