mtd: nand: fix build failure and incorrect return from omap_wait()

We need to include jiffies.h manually in some cases, and the status
returned from omap_wait() was broken in two separate ways.

Also add cond_resched() to the loop.

Signed-off-by: Vimal Singh <vimalsingh@ti.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>