fs/proc/task_mmu.c: suppress compilation warnings with W=1

fs/proc/task_mmu.c: suppress compilation warnings with W=1

Suppress a bunch of warnings of the form:

  fs/proc/task_mmu.c: In function 'show_smap_vma_flags':
  fs/proc/task_mmu.c:635:22: warning: initialized field overwritten [-Wt override-init]
     [ilog2(VM_READ)] = "rd",
                        ^~~~
  fs/proc/task_mmu.c:635:22: note: (near initialization for 'mnemonics[0]')

They happen because of the way we intentionally build the table, so
silence the warning when building with 'make W=1'.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Valdis Kletnieks <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>