mtd: nand: denali: set proper error code on timeout

The condition "if (irq_status == 0)" already ensures that one half of
the ternary ?: is dead. I think this should probably actually be a FAIL,
not a PASS.

Caught by Coverity.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Jamie Iles <jamie@jamieiles.com>