fs/exfat: do error check for d_splice_alias return

fs/exfat: do error check for d_splice_alias return

This patch adds error check in case a defect exFAT SD cards is inserted.

Change-Id: I37f6b8716abd556908aad72b18fcc7ac5719766e
Signed-off-by: Min Shi <e13386@motorola.com>
Signed-off-by: Shiyong Li <a22381@motorola.com>
Reviewed-on: https://gerrit.mot.com/1102184
SLTApproved: Slta Waiver
SME-Granted: SME Approvals Granted
Tested-by: Jira Key
Reviewed-by: Igor Kovalenko <igork@motorola.com>
Submit-Approved: Jira Key
Reviewed-on: https://gerrit.mot.com/1276885
Reviewed-by: Hua Tan <tanhua1@motorola.com>