mmc: meson-gx-mmc: Explicitly include pinctr/consumer.h

The Meson GX MMC driver fails to build after commit 23c35f48
("pinctrl: remove include file from <linux/device.h>") because it relies
on the pinctrl/consumer.h being pulled in by the device.h header
implicitly.

Include the header explicitly to avoid the build failure.

Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>