pipe: fix off-by-one error when checking buffer limits

pipe: fix off-by-one error when checking buffer limits

With pipe-user-pages-hard set to 'N', users were actually only allowed up
to 'N - 1' buffers; and likewise for pipe-user-pages-soft.

Fix this to allow up to 'N' buffers, as would be expected.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: b0b91d18e2e9 ("pipe: fix limit checking in pipe_set_size()")
Signed-off-by: Eric Biggers <[email protected]>
Acked-by: Willy Tarreau <[email protected]>
Acked-by: Kees Cook <[email protected]>
Acked-by: Joe Lawrence <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: "Luis R . Rodriguez" <[email protected]>
Cc: Michael Kerrisk <[email protected]>
Cc: Mikulas Patocka <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>