rt2x00: increase led's name buffer length

With 9-letter driver names phy's number was truncated
to two characters, which caused warnings when creating
sysfs entries for leds on systems with multiple devices.

Signed-off-by: Jakub Kicinski <kubakici@wp.pl>
Reviewed-by: Stanislaw Gruszka <sgruszka@redhat.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>