mmc: sdhci-esdhc-imx: validate pinctrl before use it

When imx_data->pinctrl is not a valid pointer, pinctrl_lookup_state
will trigger kernel panic.

When we boot Dual OS on Jailhouse hypervisor, we let the 1st Linux to
configure pinmux ready for the 2nd OS, so the 2nd OS not have pinctrl
settings.

Similar to this commit b62eee9f

 ("mmc: sdhci-esdhc-imx: no fail when no pinctrl available").

Reviewed-by: Bough Chen <haobo.chen@nxp.com>
Reviewed-by: Alice Guo <alice.guo@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Link: https://lore.kernel.org/r/1614222604-27066-6-git-send-email-peng.fan@oss.nxp.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>