parisc: fix map_pages() to actually populate upper directory

The commit d96885e2 ("parisc: use pgtable-nopXd instead of
4level-fixup") converted PA-RISC to use folded page tables, but it missed
the conversion of pgd_populate() to pud_populate() in maps_pages()
function. This caused the upper page table directory to remain empty and
the system would crash as a result.

Using pud_populate() that actually populates the page table instead of
dummy pgd_populate() fixes the issue.

Fixes: d96885e2 ("parisc: use pgtable-nopXd instead of 4level-fixup")
Reported-by: Meelis Roos <mroos@linux.ee>
Reported-by: Jeroen Roovers <jer@gentoo.org>
Reported-by: Mikulas Patocka <mpatocka@redhat.com>
Tested-by: Jeroen Roovers <jer@gentoo.org>
Tested-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/mm/init.c

@@ -401,7 +401,7 @@ static void __init map_pages(unsigned long start_vaddr,
 			pmd = (pmd_t *) __pa(pmd);
 		}
 
-		pgd_populate(NULL, pg_dir, __va(pmd));
+		pud_populate(NULL, (pud_t *)pg_dir, __va(pmd));
 #endif
 		pg_dir++;