blackfin: bf561: forgot CSYNC in get_core_lock_noflush

SMP kgdb runs into dead loop without this CSYNC when one core single
steps over get_core_lock_noflush and the other executes get_core_lock
as a slave node.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Signed-off-by: Bob Liu <lliubbo@gmail.com>