The current code checks if the next block exceeds the size of the card.
This generates an error while reading the last block of the card.
Do the out-of-bounds check when starting to read a new block to fix this.

This issue became visible with increased error checking in Linux 4.13.

Cc: qemu-stable@nongnu.org
Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
Reviewed-by: Alistair Francis <alistair.francis@xilinx.com>
Message-id: 20170916091611.10241-1-m.olbrich@pengutronix.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>