ext4: Fix ext4_ext_journal_restart() to reflect errors up to the caller

Fix ext4_ext_journal_restart() so it returns any errors reported by 
ext4_journal_extend() and ext4_journal_restart().

Signed-off-by: Shen Feng <shen@cn.fujitsu.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>