libkmod: Do not set errno in libkmod-index

libkmod: Do not set errno in libkmod-index

Don't set errno in read functions ad it's a libc interface which we
should not be overriding. None of the functions up the call stack (some
examples) check on it.

Signed-off-by: Max Kunzelmann <maxdev@posteo.de>
Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/240
[ Reword commit message according to suggestion by Emil and remove
  inline ]
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>