Use this snippet code.
function yzc_remove_profile_cover_dimensions() {
remove_filter( 'bp_attachments_get_cover_image_dimensions', 'yz_attachments_get_cover_image_dimensions' );
}
add_action( 'plugins_loaded', 'yzc_remove_profile_cover_dimensions' );
Put it on bp-custom.php file and upload on wp-content/plugins folder.