mtd: denali: remove a set-but-unused variable

The variable "retry" in wait_for_irq() is set, but not used.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>