depmod: Fix possible 0 return on error

depmod: Fix possible 0 return on error

errno may be long overwritten at this point and doesn't mean much on a
return from the cb(). Just replace with the same error we are output on
the log.

Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>
Reviewed-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Link: https://github.com/kmod-project/kmod/pull/337