greybus: sdio: change the order of remove and free mmc host

The mmc host should be removed frist. Then it
will be freed.

Signed-off-by: Phong Tran <tranmanphong@gmail.com>
Reviewed-by: Rui Miguel Silva <rui.silva@linaro.org>
Reviewed-by: Mark Greer <mgreer@animalcreek.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>