sbp2: check for ARM failure

Sbp2 did not check for successful registration of the lower address range
when CONFIG_IEEE1394_SBP2_PHYS_DMA was set. If hpsb_register_addrspace
failed, a "login timed-out" would occur which is misleading. Now sbp2 logs
a sensible error message.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Jody McIntyre <scjody@modernduck.com>