dmaengine: pxa_dma: fix the maximum requestor line

The current number of requestor lines is limited to 31. This was an
error of a previous commit, as this number is platform dependent, and is
actually :
 - for pxa25x: 40 requestor lines
 - for pxa27x: 75 requestor lines
 - for pxa3xx: 100 requestor lines

The previous testing did not reveal the faulty constant as on pxa[23]xx
platforms, only camera, MSL and USB are above requestor 32, and in these
only the camera has a driver using dma.

Fixes: e87ffbdf

 ("dmaengine: pxa_dma: fix the no-requestor case")
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Vinod Koul <vinod.koul@intel.com>