kexec: fix possible memory leak in check_reuse_initrd

If the if test is ok, then it will call die() to exit the process,
so freeing line will not be reached, causing memory leak. Fix this.

Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Simon Horman <horms@verge.net.au>