dmaengine: iop-adma: make array 'handler' static const, makes object smaller

Don't populate the array 'handler' on the stack but instead make it
static const. Makes the object code smaller by 80 bytes.

Before:
   text	   data	    bss	    dec	    hex	filename
  38225	   9084	     64	  47373	   b90d	drivers/dma/iop-adma.o

After:
   text	   data	    bss	    dec	    hex	filename
  38081	   9148	     64	  47293	   b8bd	drivers/dma/iop-adma.o

(gcc version 9.2.1, amd64)

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20190905163726.19690-1-colin.king@canonical.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>