FAT: add 'errors' mount option

On severe errors FAT remounts itself in read-only mode. Allow to
specify FAT fs desired behavior through 'errors' mount option:
panic, continue or remount read-only.

`mount -t [fat|vfat] -o errors=[panic,remount-ro,continue] \
	<bdev> <mount point>`

This is analog to ext2 fs 'errors' mount option.

Signed-off-by: Denis Karpov <ext-denis.2.karpov@nokia.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
diff --git a/fs/fat/fatent.c b/fs/fat/fatent.c
index da6eea4..60c31f7 100644
--- a/fs/fat/fatent.c
+++ b/fs/fat/fatent.c
@@ -345,7 +345,7 @@
 
 	if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
 		fatent_brelse(fatent);
-		fat_fs_panic(sb, "invalid access to FAT (entry 0x%08x)", entry);
+		fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
 		return -EIO;
 	}
 
@@ -557,7 +557,7 @@
 			err = cluster;
 			goto error;
 		} else if (cluster == FAT_ENT_FREE) {
-			fat_fs_panic(sb, "%s: deleting FAT entry beyond EOF",
+			fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
 				     __func__);
 			err = -EIO;
 			goto error;