trace: Fix alignment logic in flyrecord header

Current alignment which is using 16 bytes is not correct in connection to
trace_clocks description and it's length.
That's why use start_addr variable and record proper size based on used
entries.

Fixes: be16fc81 ("trace: Update proftool to use new binary format").
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Michal Simek <michal.simek@amd.com>
Link: https://lore.kernel.org/r/691dad64df80993ca4cfb6d0e33964ed26f50bee.1694779918.git.michal.simek@amd.com