char: Int overflow in lp_do_ioctl().

arg comes from user-space, so int overflow may occur:
	LP_TIME(minor) = arg * HZ/100;

Reported-by: Yongjian Xu <xuyongjiande@gmail.com>
Suggested-by: Qixue Xiao <s2exqx@gmail.com>
Signed-off-by: Yu Chen <chyyuu@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>