libkmod: update remaining function to return the error code

libkmod: update remaining function to return the error code

Rework the function signature and return the error code instead of the
stripped module. Thus we no longer explicitly set errno.

v2:
 - kmod_file_open() - use _cleanup_free_, return errno instead of ENOMEM

Reference: https://github.com/kmod-project/kmod/issues/244
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/346
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>