mtd: pxa3xx_nand: cleanup wait_for_completion handling

return type of wait_for_completion_timeout is unsigned long not int, this
patch uses the return value of wait_for_completion_timeout in the condition
directly rather than assigning it to an incorrect type variable.

The variable used for handling the return of wait_for_cmpletion_timeout
was int but should be unsigned long, where it was not in use for
anything else and the return value in case of completion (>0) is not
used it was removed and wait_for_completion_timeout() used directly in
the if condition.

To make the timeout values a bit simpler to read and also handle all of
the corner cases correctly the declarations are moved to
msecs_to_jiffies().

The timeout declaration cleanup is just for readability

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>