mmc: fix data timeout for SEND_EXT_CSD

Commit 0d3e0460


"MMC: CSD and CID timeout values" inadvertently broke
the timeout for the MMC command SEND_EXT_CSD.

This patch puts it back again.

Depending on the characteristics of the controller,
this bug may prevent the use of MMC cards.

Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>