ext4: fix memory leaks in error path handling of ext4_ext_zeroout()

ext4: fix memory leaks in error path handling of ext4_ext_zeroout()

commit b720303df7352d4a7a1f61e467e0a124913c0d41 upstream (as of v2.6.34-git13)

When EIO occurs after bio is submitted, there is no memory free
operation for bio, which results in memory leakage. And there is also
no check against bio_alloc() for bio.

Acked-by: Dave Kleikamp <shaggy@linux.vnet.ibm.com>
Signed-off-by: Jing Zhang <zj.barak@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>