documentation/devicetree: Fix a typo in exynos-dw-mshc.txt

Fixed a typo in referenced file name.

Cc: Thomas Abraham <thomas.abraham@linaro.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>

Documentation/devicetree/bindings/mmc/exynos-dw-mshc.txt

@@ -4,7 +4,7 @@
 The Synopsis designware mobile storage host controller is used to interface
 a SoC with storage medium such as eMMC or SD/MMC cards. This file documents
 differences between the core Synopsis dw mshc controller properties described
-by synposis-dw-mshc.txt and the properties used by the Samsung Exynos specific
+by synopsis-dw-mshc.txt and the properties used by the Samsung Exynos specific
 extensions to the Synopsis Designware Mobile Storage Host Controller.
 
 Required Properties: