mmc: sdhci-esdhc-imx: merge the same register check into one place

In esdhc_writel_le() function, there's duplicated checking of the same
register as follows:
"if (unlikely(reg == SDHCI_INT_ENABLE || reg == SDHCI_SIGNAL_ENABLE))".
Merge them into one and remove the duplicated one.

Signed-off-by: Dong Aisheng <aisheng.dong@freescale.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>