Hang on reboot in nand_get_device()

[Andrew E. Mileski]

I'm experiencing a hang on reboot with a Freescale P1022 PowerPC system, with a
dual chip-select NAND part (specified in the device tree as two separate 
devices), and kernel v4.0.6.

It appears to be a hang in mtd/nand/nand_base.c:nand_get_device() waiting on
chip->controller->active.

Shouldn't nand_shutdown(), or perhaps a special case in nand_get_device() for
FL_SHUTDOWN, set chip->controller->active = NULL before returning?

This seems to fix the problem for me, but I don't know all the code well enough
to know whether doing so is appropriate, or sufficient.

~~Andrew E. Mileski