UPSTREAM: debugfs: convert gid= argument from decimal, not octal

UPSTREAM: debugfs: convert gid= argument from decimal, not octal

This patch technically breaks userspace, but I suspect that anyone who
actually used this flag would have encountered this brokenness, declared
it lunacy, and already sent a patch.

Signed-off-by: Dave Reisner <dreisner@archlinux.org>
Reviewed-by: Vasiliy Kulikov <segoon@openwall.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
BUG=chromium-os:23758
TEST=link build, debugfs mount options work with decimal for gid

Change-Id: I4a37f3bd13da0ced916bde8038de16ebc3504d5e
(cherry picked from upstream commit f1688e0431d3a395388e70fe21da89ed0de0c323)
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/42650
Reviewed-by: Mandeep Singh Baines <msb@chromium.org>