UPSTREAM: mm: Fix TLB flush for not-first PFNMAP mappings in unmap_region()

This is a stable-specific patch.
I botched the stable-specific rewrite of
commit b67fbebd4cf98 ("mmu_gather: Force tlb-flush VM_PFNMAP vmas"):
As Hugh pointed out, unmap_region() actually operates on a list of VMAs,
and the variable "vma" merely points to the first VMA in that list.
So if we want to check whether any of the VMAs we're operating on is
PFNMAP or MIXEDMAP, we have to iterate through the list and check each VMA.

Bug: 245812080
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 3998dc50ebdc127ae79b10992856fb76debc2005)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: Ib8ddb51815e53f42daec5d98a196866a078a7550