mm/mmap.c: use while instead of if+goto

mm/mmap.c: use while instead of if+goto

The creators of the C language gave us the while keyword. Let's use
that instead of synthesizing it from if+goto.

Made possible by 6597d783397a ("mm/mmap.c: replace find_vma_prepare()
with clearer find_vma_links()").

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Roman Gushchin <klamm@yandex-team.ru>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>