mmc: block: don't start new request when the card is removed

It's not necessary to start a new request while error handling if
the card was removed.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Konstantin Dorfman <kdorfman@codeaurora.org>
Signed-off-by: Chris Ball <cjb@laptop.org>