mmc: sdhci-esdhc-imx: do not touch other bit when config DTOCV

Now, when call esdhc_set_timeout() to set the data timeout counter value,
IPP_RST_N(bit 23) is wrongly affected. This patch add a mask to avoid this.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>