If arch_validate_hwbkpt_settings() fails, bp->ctx won't be valid and the
kernel panics. Add a check to fix this.
Reported-by: NEdjunior Barbosa Machado <emachado@linux.vnet.ibm.com>
Signed-off-by: NNaveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>