mmc: cast u8 to unsigned long long to avoid unexpected error

card->ext_csd.enhanced_area_offset is defined as "unsigned long long",
and, ext_csd[] is defined as u8.
unsigned long long data might have strange data if first bit of ext_csd[]
was 1. this patch cast it to (unsigned long long)
Special thanks to coverity <http://www.coverity.com>

ex)
        u8  data8;
        u64 data64;

        data8 = 0x80;
        data64 = (data8 << 24); // 0xffffffff80000000
        data64 = (((unsigned long long)data8) << 24); // 0x80000000;

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/mmc.c

@@ -267,8 +267,10 @@ static void mmc_manage_enhanced_area(struct mmc_card *card, u8 *ext_csd)
 			 * calculate the enhanced data area offset, in bytes
 			 */
 			card->ext_csd.enhanced_area_offset =
-				(ext_csd[139] << 24) + (ext_csd[138] << 16) +
-				(ext_csd[137] << 8) + ext_csd[136];
+				(((unsigned long long)ext_csd[139]) << 24) +
+				(((unsigned long long)ext_csd[138]) << 16) +
+				(((unsigned long long)ext_csd[137]) << 8) +
+				(((unsigned long long)ext_csd[136]));
 			if (mmc_card_blockaddr(card))
 				card->ext_csd.enhanced_area_offset <<= 9;
 			/*