/proc/pid/maps: don't show pgoff of pure ANON VMAs

/proc/pid/maps: don't show pgoff of pure ANON VMAs

Recently, it's argued that what proc/pid/maps shows is ugly when a 32bit
binary runs on 64bit host.

/proc/pid/maps outputs vma's pgoff member but vma->pgoff is of no use
information is the vma is for ANON.  With this patch, /proc/pid/maps shows
just 0 if no file backing store.

[[email protected]: coding-style fixes]
[[email protected]: coding-style fixes]
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Mike Waychison <[email protected]>
Reported-by: Ying Han <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>