resource: make alloc_free_mem_region() works for iomem_resource

During developing a kunit test case for region_intersects(), some fake
resources need to be inserted into iomem_resource.  To do that, a resource
hole needs to be found first in iomem_resource.

However, alloc_free_mem_region() cannot work for iomem_resource now. 
Because the start address to check cannot be 0 to detect address wrapping
0 in gfr_continue(), while iomem_resource.start == 0.  To make
alloc_free_mem_region() works for iomem_resource, gfr_start() is changed
to avoid to return 0 even if base->start == 0.  We don't need to check 0
as start address.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Davidlohr Bueso <[email protected]>
Cc: Jonathan Cameron <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Alison Schofield <[email protected]>
Cc: Vishal Verma <[email protected]>
Cc: Ira Weiny <[email protected]>
Cc: Alistair Popple <[email protected]>
Cc: Andy Shevchenko <[email protected]>
Cc: Bjorn Helgaas <[email protected]>
Cc: Baoquan He <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

kernel/resource.c

@@ -1830,7 +1830,7 @@ static resource_size_t gfr_start(struct resource *base, resource_size_t size,
 		return end - size + 1;
 	}
 
-	return ALIGN(base->start, align);
+	return ALIGN(max(base->start, align), align);
 }
 
 static bool gfr_continue(struct resource *base, resource_size_t addr,