block/nand: Formatting sweep

Make this code closer to passing checkpatch. Mostly missing braces, but
a few rogue tabs in there as well.

Cc: qemu-trivial@nongnu.org

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
