doc: device_setup: fix generic_linux device_config example

A copy/paste of the documentation example results in a python
backtrace because the dict keys cannot be quoted:

    wlauto.exceptions.ConfigError: Sytax error in config: keyword can't be an expression (config.py, line XYZ)

Fix by removing the quotes from the keys in the example.

Signed-off-by: Kevin Hilman <khilman@linaro.org>

doc/source/device_setup.rst

@@ -363,11 +363,11 @@ A typical ``device_config`` inside ``config.py`` may look something like
 .. code-block:: python
 
         device_config = dict(
-                'host'='192.168.0.7',
-                'username'='guest',
-                'password'='guest',
-                'core_names'=['a7', 'a7', 'a7', 'a15', 'a15'],
-                'core_clusters'=[0, 0, 0, 1, 1],
+                host='192.168.0.7',
+                username='guest',
+                password='guest',
+                core_names=['a7', 'a7', 'a7', 'a15', 'a15'],
+                core_clusters=[0, 0, 0, 1, 1],
                 # ...
         )