target: Fix typo in drivers/target

Correct spelling "exeeds" to "exceeds" in iscsi/iscsi_target_nego.c
Correct spelling "diabled" to "disabled" in target_core_configfs.c

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>