vfs: fix put_compat_statfs64() does not handle errors

vfs: fix put_compat_statfs64() does not handle errors

put_compat_statfs64() does NOT return -1 and setting errno to EOVERFLOW
when some variables(like: f_bsize) overflowed in the returned struct.

The reason is that the ubuf->f_blocks is __u64 type, it couldn't be
4bits as the judgement in put_comat_statfs64(). Here correct the
__u32 variables(in struct compat_statfs64) for comparison.

reproducer:
step1. mount hugetlbfs with two different pagesize on ppc64 arch.

$ hugeadm --pool-pages-max 16M:0
$ hugeadm --create-mount
$ mount | grep -i hugetlbfs
none on /var/lib/hugetlbfs/pagesize-16MB type hugetlbfs (rw,relatime,seclabel,pagesize=16777216)
none on /var/lib/hugetlbfs/pagesize-16GB type hugetlbfs (rw,relatime,seclabel,pagesize=17179869184)

step2. compile & run this C program.

$ cat statfs64_test.c

 #define _LARGEFILE64_SOURCE
 #include <stdio.h>
 #include <sys/syscall.h>
 #include <sys/statfs.h>

 int main()
 {
	struct statfs64 sb;
	int err;

	err = syscall(SYS_statfs64, "/var/lib/hugetlbfs/pagesize-16GB", sizeof(sb), &sb);
	if (err)
		return -1;

	printf("sizeof f_bsize = %d, f_bsize=%ld\n", sizeof(sb.f_bsize), sb.f_bsize);

	return 0;
 }

$ gcc -m32 statfs64_test.c
$ ./a.out
sizeof f_bsize = 4, f_bsize=0

Signed-off-by: Li Wang <liwang@redhat.com>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>