feat(handoff): update register signature

The existing register signature was changed from 0x6ed0ff to account for
0xff being a value that is regularly found in memory [1].

[1] https://github.com/sjg20/firmware_handoff/commit/f70c184905607f6b1d074a5de9aa407a5d92344b

Change-Id: Ib217f1b68df9e534fc61604c88eea4560ecb9dc2
Signed-off-by: Harrison Mutai <harrison.mutai@arm.com>
2 files changed