mmc: allow for MMC v4.4

JEDEC eMMC specification version 4.4 (MMCA 4.4) defines Extended CSD
structure versions up to 5.

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>