mmc: unbreak sdhci-esdhc-imx on i.MX25

This was broken by me in 37865fe9
("mmc: sdhci-esdhc-imx: fix timeout on i.MX's sdhci") where more
extensive tests would have shown that read or write of data to the
card were failing (even if the partition table was correctly read).

Signed-off-by: Eric Bénard <eric@eukrea.com>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Chris Ball <cjb@laptop.org>