ext4: add error processing when calling ext4_mb_init_cache in mballoc

Add error processing for ext4_mb_load_buddy when it calls
ext4_mb_init_cache.

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>