libkmod-module: convert return value from system() to errno
libkmod-module: convert return value from system() to errno

Don't use exit status of a command directly as errno code, callers
will be confused.

Signed-off-by: Topi Miettinen <a268306c458d691fe7f5afe3a1e6d5ebba59e89f@gmail.com>

lucasdemarchi/kmod,lucasdemarchi/kmod,lucasdemarchi/kmod