api: mraa: gpio: Fix doxygen warning

This commit fixes the below doxygen warning:

"warning: unexpected token in comment block while parsing the argument of command param"

Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

api/mraa/gpio.hpp

@@ -347,7 +347,7 @@ class Gpio
     /**
      * Change Gpio output driver mode
      *
-     * @param mode @param mode Set output driver mode
+     * @param mode Set output driver mode
      * @return Result of operation
      */
     Result