fat: use fat_msg_ratelimit() in fat__get_entry()

If an application tries to lookup (opendir/readdir/stat) 5000 files on a
fatfs USB device and the device is unplugged, many message occur, shown
below.  This makes the application slow.  So use the new
fat_msg_ratelimit() decrease the messaging rate.

  #> ./file_lookup_testcase ./files_directory/
  usb 2-1.4: USB disconnect, device number 4
  FAT-fs (sda1): FAT read failed (blocknr 2631)
  FAT-fs (sda1): Directory bread(block 396816) failed
  FAT-fs (sda1): Directory bread(block 396817) failed
  FAT-fs (sda1): Directory bread(block 396818) failed
  FAT-fs (sda1): Directory bread(block 396819) failed
  FAT-fs (sda1): Directory bread(block 396820) failed
  FAT-fs (sda1): Directory bread(block 396821) failed
  FAT-fs (sda1): Directory bread(block 396822) failed
  FAT-fs (sda1): Directory bread(block 396823) failed
  FAT-fs (sda1): Directory bread(block 406824) failed
  FAT-fs (sda1): Directory bread(block 406825) failed
  FAT-fs (sda1): Directory bread(block 406826) failed
  FAT-fs (sda1): Directory bread(block 406827) failed
  FAT-fs (sda1): Directory bread(block 406828) failed
  FAT-fs (sda1): Directory bread(block 406829) failed
  FAT-fs (sda1): Directory bread(block 406830) failed
  FAT-fs (sda1): Directory bread(block 406831) failed
  FAT-fs (sda1): Directory bread(block 417696) failed
  FAT-fs (sda1): Directory bread(block 417697) failed
  FAT-fs (sda1): Directory bread(block 417698) failed
  FAT-fs (sda1): Directory bread(block 417699) failed
  FAT-fs (sda1): Directory bread(block 417700) failed
  FAT-fs (sda1): Directory bread(block 417701) failed
  FAT-fs (sda1): Directory bread(block 417702) failed
  FAT-fs (sda1): Directory bread(block 417703) failed
  FAT-fs (sda1): FAT read failed (blocknr 2631)
  FAT-fs (sda1): Directory bread(block 396816) failed
  FAT-fs (sda1): Directory bread(block 396817) failed
  FAT-fs (sda1): Directory bread(block 396818) failed
  FAT-fs (sda1): Directory bread(block 396819) failed
  FAT-fs (sda1): Directory bread(block 396820) failed
  FAT-fs (sda1): Directory bread(block 396821) failed

Signed-off-by: Namjae Jeon <linkinjeon@gmail.com>
Signed-off-by: Amit Sahrawat <amit.sahrawat83@gmail.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>