ext4: replace __FUNCTION__ occurrences

__FUNCTION__ is gcc-specific, use __func__ instead

Signed-off-by: Stoyan Gaydarov <stoyboyker@gmail.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>