fs/exfat: link superblock for all the buffer head

fs/exfat: link superblock for all the buffer head

Otherwise, we can get kernel panic when handling fs_error().

Change-Id: I288ece9bdc0182b0d4cf23f1bba920d341a8f540
Signed-off-by: Jaegeuk Kim <jaegeuk@motorola.com>
Signed-off-by: Shiyong Li <a22381@motorola.com>
Reviewed-on: https://gerrit.mot.com/1102177
SME-Granted: SME Approvals Granted
SLTApproved: Slta Waiver
Tested-by: Jira Key
Reviewed-by: Igor Kovalenko <igork@motorola.com>
Submit-Approved: Jira Key
Reviewed-on: https://gerrit.mot.com/1276878
Reviewed-by: Hua Tan <tanhua1@motorola.com>