hamradio: Remove unnecessary strscpy_pad() size arguments

If the destination buffer has a fixed length, strscpy_pad()
automatically determines its size using sizeof() when the argument is
omitted. This makes the explicit sizeof() calls unnecessary - remove
them.

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Link: https://patch.msgid.link/20250407082607.741919-2-thorsten.blum@linux.dev


Signed-off-by: Paolo Abeni <pabeni@redhat.com>