Don't deselect the card too soon. To set the block size or switch the
function parameters, the card has to be in transfer state. If it is in
the idle state, the commands are ignored. This caused us not to set
the proper parameters that we later assume to be present, leading to
downstream failures of the card / interface as our state machine
mismatches the card's.

Submitted by: Svatopluk Kraus <onwahe at gmail.com>, Michal Meloun
<meloun at miracle.cz>