mmc: print an error on FLUSH timeout

Up until now the FLUSH timeout error was not printed and there
was no way to know if the FLUSH completed successfully or not.
Printing the FLUSH failure will help to identify if FS corruption
happened due to this timeout.

Change-Id: Ibbb51d030d7130d63974a1b4319ad4a24621c595
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Konstantin Dorfman <kdorfman@codeaurora.org>