staging: goldfish: document mutex usage

Coding style: document mutex usage
Signed-off-by: Loic Pefferkorn <loic@loicp.eu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/goldfish/goldfish_nand.c

@@ -31,6 +31,7 @@
 #include "goldfish_nand_reg.h"
 
 struct goldfish_nand {
+	/* lock protects access to the device registers */
 	struct mutex            lock;
 	unsigned char __iomem  *base;
 	struct cmd_params       *cmd_params;