Documentation: dt: keystone: Fix up missing quotes

Add missing commits for the suggest compatible flags in dt binding.

Fixes: 8841cbf666d6 ("Documentation: dt: keystone: provide SoC specific compatible flags")
Reported-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>

Documentation/devicetree/bindings/arm/keystone/keystone.txt

@@ -17,11 +17,11 @@ SoC families:
 SoCs:
 
 - Keystone 2 Hawking/Kepler
-   compatible = ti,k2hk", "ti,keystone"
+   compatible = "ti,k2hk", "ti,keystone"
 - Keystone 2 Lamarr
-   compatible = ti,k2l", "ti,keystone"
+   compatible = "ti,k2l", "ti,keystone"
 - Keystone 2 Edison
-   compatible = ti,k2e", "ti,keystone"
+   compatible = "ti,k2e", "ti,keystone"
 
 Boards:
 -  Keystone 2 Hawking/Kepler EVM