mm/memory_hotplug: use pgprot_val to get value of pgprot

pgprot.pgprot is non-portable code.  It should be replaced by portable
macro pgprot_val.

Link: https://lkml.kernel.org/r/20220426071302.220646-1-liusongtang@huawei.comSigned-off-by: liusongtang <liusongtang@huawei.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Xiaoming Ni <nixiaoming@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory_hotplug.c

@@ -303,7 +303,7 @@ int __ref __add_pages(int nid, unsigned long pfn, unsigned long nr_pages,
 	int err;
 	struct vmem_altmap *altmap = params->altmap;
 
-	if (WARN_ON_ONCE(!params->pgprot.pgprot))
+	if (WARN_ON_ONCE(!pgprot_val(params->pgprot)))
 		return -EINVAL;
 
 	VM_BUG_ON(!mhp_range_allowed(PFN_PHYS(pfn), nr_pages * PAGE_SIZE, false));