luci-mod-status: fix syslog / dmesg scroll for some themes

The actual code moves the scroll in the window. This works for the bootstrap theme, because the scroll is at window level. But this does not work for other themes, like material.

This commit changes the move of the scroll by "focusing" the window in the opposite button element in the syslog / dmesg page. In this way the move is automatically done by the browser.

Another solution is to "search" in the parent until we find the scroll and move it, but seems less solid.

Signed-off-by: Miguel Angel Mulero Martinez <migmul@gmail.com>