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/20240906030713.204292-3-ying.huang@intel.comSigned-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Baoquan He <bhe@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>