xfs: don't use __GFP_NOFAIL in xfs_init_fs_context

With enough debug options enabled, struct xfs_mount is larger
than 4k and thus NOFAIL allocations won't work for it.

xfs_init_fs_context is early in the mount process, and if we really
are out of memory there we'd better give up ASAP anyway.

Fixes: 7b77b46a ("xfs: use kmem functions for struct xfs_mount")
Reported-by:  <syzbot+359a67b608de1ef72f65@syzkaller.appspotmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>