net: wireless: ipw2x00: ipw2200.c: Cleaning up missing null-terminate after strncpy call

Added a guaranteed null-terminate after call to strncpy.

Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: John W. Linville <linville@tuxdriver.com>