ARM: dts: Fix compatible for ti81xx uarts for 8250

[ Upstream commit f62280efe8934a1275fd148ef302d1afec8cd3df ]

When using 8250_omap driver, we need to specify the right
compatible value for the UART to work on dm814x and dm816x.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>