mmc/omap_hsmmc: add a const qualifier

This prepares *of_device_id.data becoming const. Without this change
the following warning would occur:

	drivers/mmc/host/omap_hsmmc.c: In function 'omap_hsmmc_probe':
	drivers/mmc/host/omap_hsmmc.c:1808: warning: initialization discards qualifiers from pointer target type
Acked-by: Venkatraman S <svenkatr@ti.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/mmc/host/omap_hsmmc.c

@@ -1782,7 +1782,7 @@ static int __devinit omap_hsmmc_probe(struct platform_device *pdev)
 	if (match) {
 		pdata = of_get_hsmmc_pdata(&pdev->dev);
 		if (match->data) {
-			u16 *offsetp = match->data;
+			const u16 *offsetp = match->data;
 			pdata->reg_offset = *offsetp;
 		}
 	}