I modified your code just a bit. See if this works
if ( ! function_exists( 'the_post_limit' ) ) {
if ( true == get_theme_mod( 'the_post_limit', true ) ) {
function the_post_limit( $query ) {
if ( is_admin() || ! $query->is_main_query() )
return;
if ( is_home() ) {
// Display only 1 post for the original blog archive
$get_default_posts_per_page = get_option( 'posts_per_page' );
$query->set( 'posts_per_page', $get_default_posts_per_page );
return;
}
}
add_action( 'pre_get_posts', 'the_post_limit', 1 );
}
}