ptp: ocp: Refactor signal_show() and fix %ptT misuse

ptp: ocp: Refactor signal_show() and fix %ptT misuse

Refactor signal_show() to avoid sequential calls to sysfs_emit*()
and use the same pattern to get the index of a signal as it's done
in signal_store().

While at it, fix wrong use of %ptT against struct timespec64.
It's kinda lucky that it worked just because the first member
there 64-bit and it's of time64_t type. Now with %ptS it may
be used correctly.

Reviewed-by: Vadim Fedorenko <vadim.fedorenko@linux.dev>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://patch.msgid.link/20251124084816.205035-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>