mmc: core: Remove redundant code in mmc_send_cid()

The mmc_send_cid() is never called using non SPI mode. Thus, let's remove
the redundant code dealing with this.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>