ext4: Fix buffer head leaks after calls to ext4_get_inode_loc()

Calls to ext4_get_inode_loc() returns with a reference to a buffer
head in iloc->bh.  The callers of this function in ext4_write_inode()
when in no journal mode and in ext4_xattr_fiemap() don't release the
buffer head after using it.

Addresses-Google-Bug: #2548165

Signed-off-by: Curt Wohlgemuth <curtw@google.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>