mtd: nand: denali: fix comment of denali_nand_info::flash_mem

The same comment "Mapped io reg base address" for flash_reg and
flash_mem probably due to the mistake of copy-paste work.
Of course, the latter is not the register base address.

Reword the comments using the terminology in the Denali User's Guide.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: NBoris Brezillon <boris.brezillon@free-electrons.com>

drivers/mtd/nand/denali.h

@@ -351,8 +351,8 @@ struct denali_nand_info {
 	struct device *dev;
 	int total_used_banks;
 	uint16_t page;
-	void __iomem *flash_reg;  /* Mapped io reg base address */
-	void __iomem *flash_mem;  /* Mapped io reg base address */
+	void __iomem *flash_reg;	/* Register Interface */
+	void __iomem *flash_mem;	/* Host Data/Command Interface */
 
 	/* elements used by ISR */
 	struct completion complete;