mei: trace: treat reg parameter as string

mei: trace: treat reg parameter as string

The commit
afd2627f727b ("tracing: Check "%s" dereference via the field and not the TP_printk format")
forbids to emit event with a plain char* without a wrapper.

The reg parameter always passed as static string and wrapper
is not strictly required, contrary to dev parameter.
Use the string wrapper anyway to check sanity of the reg parameters,
store it value independently and prevent internal kernel data leaks.

Since some code refactoring has taken place, explicit backporting may
be needed for kernels older than 6.10.

Cc: stable@vger.kernel.org  # v6.11+
Fixes: a0a927d06d79 ("mei: me: add io register tracing")
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Link: https://patch.msgid.link/20260111145125.1754912-1-alexander.usyskin@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>