mmc: core: cd_label must be last entry of mmc_gpio struct

commit bfd694d5 ("mmc: core: Add tunable delay
before detecting card after card is inserted") adds
"u32 cd_debounce_delay_ms" to the last of mmc_gpio
struct and cause "char cd_label[0]" NOT work as string
pointer of card detect label, when "cat /proc/interrupts",
the devname for card detect gpio is incorrect as below:

144:          0  gpio-mxc  22 Edge      ▒
161:          0  gpio-mxc   7 Edge      ▒

Move the cd_label field down to fix this, and drop the
zero from the array size to prevent future similar bugs,
the result is correct as below:

144:          0  gpio-mxc  22 Edge      2198000.mmc cd
161:          0  gpio-mxc   7 Edge      2190000.mmc cd

Fixes: bfd694d5 ("mmc: core: Add tunable delay before detecting card after card is inserted")
Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Tested-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>