mtd: maps: sc520cdp: fix warnings

On m86k, and maybe a few other architectures, we get this kind of
warning, due to misuse of volatile:

   drivers/mtd/maps/sc520cdp.c: In function 'sc520cdp_setup_par':
>> drivers/mtd/maps/sc520cdp.c:223:2: warning: passing argument 1 of 'iounmap' discards 'volatile' qualifier from pointer target type [enabled by default]
   arch/m68k/include/asm/raw_io.h:22:13: note: expected 'void *' but argument is of type 'volatile long unsigned int *'

Rather than annotating the variable declaration, let's just use the
proper accessors, which add the 'volatile' qualifier to the operation.
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/maps/sc520cdp.c

@@ -183,7 +183,7 @@ static const struct sc520_par_table par_table[NUM_FLASH_BANKS] =
 
 static void sc520cdp_setup_par(void)
 {
-	volatile unsigned long __iomem *mmcr;
+	unsigned long __iomem *mmcr;
 	unsigned long mmcr_val;
 	int i, j;
 
@@ -203,11 +203,11 @@ static void sc520cdp_setup_par(void)
 	*/
 	for(i = 0; i < NUM_FLASH_BANKS; i++) {		/* for each par_table entry  */
 		for(j = 0; j < NUM_SC520_PAR; j++) {	/* for each PAR register     */
-			mmcr_val = mmcr[SC520_PAR(j)];
+			mmcr_val = readl(&mmcr[SC520_PAR(j)]);
 			/* if target device field matches, reprogram the PAR */
 			if((mmcr_val & SC520_PAR_TRGDEV) == par_table[i].trgdev)
 			{
-				mmcr[SC520_PAR(j)] = par_table[i].new_par;
+				writel(par_table[i].new_par, &mmcr[SC520_PAR(j)]);
 				break;
 			}
 		}