mm, gup: fix typo in gup_p4d_range()

gup_p4d_range() should call gup_pud_range(), not itself.

[ This was not noticed on x86: this is the HAVE_GENERIC_RCU_GUP code
  used by arm[64] and powerpc    - Linus ]

Fixes: c2febafc6773 ("mm: convert generic code to 5-level paging")
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reported-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Reported-by: Anton Blanchard <anton@samba.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/gup.c

@@ -1455,7 +1455,7 @@ static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end,
 			if (!gup_huge_pd(__hugepd(p4d_val(p4d)), addr,
 					 P4D_SHIFT, next, write, pages, nr))
 				return 0;
-		} else if (!gup_p4d_range(p4d, addr, next, write, pages, nr))
+		} else if (!gup_pud_range(p4d, addr, next, write, pages, nr))
 			return 0;
 	} while (p4dp++, addr = next, addr != end);