mmc: dw_mmc: Zap endless timeout

Endless timeouts are bad, since if we get stuck in one, we have no
way out. Zap this one by implementing proper timeout.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Dinh Nguyen <dinguyen@opensource.altera.com>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Cc: Tom Rini <trini@konsulko.com>