powerpc/vmemmap: Don't warn if we don't find a mapping vmemmap list entry

Now that we are handling vmemmap list allocation failure correctly, don't
WARN in section deactivate when we don't find a mapping vmemmap list entry.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200731113500.248306-2-aneesh.kumar@linux.ibm.com

arch/powerpc/mm/init_64.c

@@ -285,10 +285,8 @@ static unsigned long vmemmap_list_free(unsigned long start)
 		vmem_back_prev = vmem_back;
 	}
 
-	if (unlikely(!vmem_back)) {
-		WARN_ON(1);
+	if (unlikely(!vmem_back))
 		return 0;
-	}
 
 	/* remove it from vmemmap_list */
 	if (vmem_back == vmemmap_list) /* remove head */