fix PATH_MAX conditional compilation

PATH_MAX is used elsewhere in the qemu source tree without protection.

In addtion the actual code would not compile if PATH_MAX is not defined

Last the free() call is wrong as p is not malloc()ed.

Signed-off-by: Jean-Christophe Dubois <jcd@tribudubois.net>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
