mmc: sdhci-esdhc-imx: fix cpas over write issue

We should use '|=' instead '=', or it may over write the original
caps assigned before this line.

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>