thinkpad_acpi: fix possible NULL pointer dereference if kstrdupfor ec_version_str failed

[Jan Lieskovsky]

Hello guys,

  apologize for bothering you if wrong, but based on patch from Cyrill:

http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=90fe17f4df2f830601ffd422b11d1f7f9a9d0355

There is a potential NULL pointer dereference in thinkpad_acpi_module_exit() -- in case,
kstrdup for thinkpad_id.ec_version_str failed.

Kind regards
Jan Lieskovsky
--- linux-2.6.25.3.old/drivers/misc/thinkpad_acpi.c	2008-05-12 11:43:16.000000000 +0200
+++ linux-2.6.25.3/drivers/misc/thinkpad_acpi.c	2008-05-16 11:20:48.000000000 +0200
@@ -6072,7 +6072,8 @@
 		remove_proc_entry(TPACPI_PROC_DIR, acpi_root_dir);
 
 	kfree(thinkpad_id.bios_version_str);
-	kfree(thinkpad_id.ec_version_str);
+	if (thinkpad_id.ec_version_str)	
+	      	kfree(thinkpad_id.ec_version_str);
 	kfree(thinkpad_id.model_str);
 }