sh: Zero-out coherent buffer in consistent_alloc().

Be sure to zero out the buffer, this was causing occasional problems
under heavier PCI tests.

Signed-off-by: Paul Mundt <[e-mail]>

arch/sh/mm/consistent.c

···
 	split_page(page, order);
 
 	ret = page_address(page);
+	memset(ret, 0, size);
 	*handle = virt_to_phys(ret);
 
 	/*