ACPI: use kstrdup()

 Use kstrdup rather than duplicating its implementation

 The semantic patch that makes this output is available
 in scripts/coccinelle/api/kstrdup.cocci.

 More information about semantic patching is available at
 http://coccinelle.lip6.fr/



Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Signed-off-by: Len Brown <len.brown@intel.com>