mtd: cfi_cmdset_0002: allow retry/timeout loop to exit

The variable 'retries' is never modified, so if the reset operation
never is going to complete, we'll get stuck in an infinite loop.

It looks like the intention was to decrement 'retries' on every loop.
Untested.

Caught by Coverity.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>