fat: fix VFAT compat ioctls on 64-bit systems

fat: fix VFAT compat ioctls on 64-bit systems

If you compile and run the below test case in an msdos or vfat directory on
an x86-64 system with -m32 you'll get garbage in the kernel_dirent struct
followed by a SIGSEGV.

The patch fixes this.

Reported and initial fix by Bart Oldeman

#include <sys/types.h>
#include <sys/ioctl.h>
#include <dirent.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
struct kernel_dirent {
         long            d_ino;
         long		d_off;
         unsigned short  d_reclen;
         char            d_name[256]; /* We must not include limits.h! */
};
#define VFAT_IOCTL_READDIR_BOTH  _IOR('r', 1, struct kernel_dirent [2])
#define VFAT_IOCTL_READDIR_SHORT  _IOR('r', 2, struct kernel_dirent [2])

int main(void)
{
         int fd = open(".", O_RDONLY);
         struct kernel_dirent de[2];

         while (1) {
                 int i = ioctl(fd, VFAT_IOCTL_READDIR_BOTH, (long)de);
                 if (i == -1) break;
                 if (de[0].d_reclen == 0) break;
                 printf("SFN: reclen=%2d off=%d ino=%d, %-12s",
 		       de[0].d_reclen, de[0].d_off, de[0].d_ino, de[0].d_name);
 		if (de[1].d_reclen)
 		  printf("\tLFN: reclen=%2d off=%d ino=%d, %s",
 		    de[1].d_reclen, de[1].d_off, de[1].d_ino, de[1].d_name);
 		printf("\n");
         }
         return 0;
}

Signed-off-by: Bart Oldeman <bartoldeman@users.sourceforge.net>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>