doxygen: use correct comment syntax

This issue was caused by uncrustify not correctly converting the doxygen
comments.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Change-Id: Ie6dc3b057a08603b670cb27312e5f0d989426e6c
Reviewed-on: http://openocd.zylin.com/431
Tested-by: jenkins

src/flash/nand/driver.h

@@ -90,7 +90,7 @@ struct nand_flash_controller {
  */
 struct nand_flash_controller *nand_driver_find_by_name(const char *name);
 
-/* / Signature for callback functions passed to nand_driver_walk */
+/** Signature for callback functions passed to nand_driver_walk */
 typedef int (*nand_driver_walker_t)(struct nand_flash_controller *c, void *);
 /**
  * Walk the list of drivers, encapsulating the data structure type.