Revert change to fsl,mpc8641 example

Commit 7d888a0, "Aesthetic/grammar fixes to first part of
devicetree-basics.rst" changed one of the Freescale compatible examples
from "fsl,mpc8641-uart" to "fsl,ns16550". However, there is value in
using examples from real hardware when possible, and to also show that
different strings (mpc8641-uart vs. ns16550) for a device is normal, so
revert that hunk.

Signed-off-by: Grant Likely <[email protected]>
Cc: Robert P. J. Day <[email protected]>

Author: glikely

source/devicetree-basics.rst

@@ -469,10 +469,10 @@ Description:
 
 Example:
 
-   ``compatible = "fsl,ns16550", "ns16550";``
+   ``compatible = "fsl,mpc8641", "ns16550";``
 
    In this example, an operating system would first try to locate a device
-   driver that supported fsl,ns16550. If a driver was not found, it
+   driver that supported fsl,mpc8641. If a driver was not found, it
    would then try to locate a driver that supported the more general
    ns16550 device type.