book3s64/radix : Handle error conditions properly in radix_vmemmap_populate

Error conditions are not handled properly if altmap is not present
and PMD_SIZE vmemmap_alloc_block_buf fails.

In this patch, if vmemmap_alloc_block_buf fails in the non-altmap
case, we will fall back to the base mapping.

Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Donet Tom <donettom@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/7f95fe91c827a2fb76367a58dbea724e811fb152.1750593372.git.donettom@linux.ibm.com

Author: donettom-1

arch/powerpc/mm/book3s64/radix_pgtable.c

@@ -1173,7 +1173,7 @@ int __meminit radix__vmemmap_populate(unsigned long start, unsigned long end, in
 				vmemmap_set_pmd(pmd, p, node, addr, next);
 				pr_debug("PMD_SIZE vmemmap mapping\n");
 				continue;
-			} else if (altmap) {
+			} else {
 				/*
 				 * A vmemmap block allocation can fail due to
 				 * alignment requirements and we trying to align