tools/rv: Ensure monitor name and desc are NUL-terminated

tools/rv: Ensure monitor name and desc are NUL-terminated

ikm_fill_monitor_definition() copies monitor name and description with
strncpy(), but does not guarantee NUL termination when source strings are
equal to or longer than the destination buffers.

Clamp copies to sizeof(dst) - 1 and explicitly append '\0' for both fields
to keep them safe for later string operations.

Suggested-by: unknownbbqrx <dev@unknownbbqr.xyz>
Fixes: 6d60f89691fc9 ("tools/rv: Add in-kernel monitor interface")
Link: https://lore.kernel.org/r/20260604120946.90302-2-gmonaco@redhat.com
Signed-off-by: Gabriele Monaco <gmonaco@redhat.com>