BACKPORT: FROMGIT: mm: Use static initialisers for immutable fields of 'struct vm_fault'

In preparation for const-ifying the anonymous struct field of
'struct vm_fault', ensure that it is initialised using designated
initialisers.

Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Change-Id: Ib2c84bbc4d59fe1811465e59c89f8eb7f73e6229
Bug: 171278850
(cherry picked from commit 8c63ca5b
https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/faultaround

)
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>