mtd: nand: pxa3xx: Allow devices with no dma resources

When use_dma=0 there's no point in requesting resources for dma,
since they won't be used anyway. Therefore we remove that requirement,
therefore allowing devices without dma to pass the driver probe.

Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Tested-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>