ACPI: acpi_os_get_thread_id() returns current

Linux mutexes and the debug code that that reference
acpi_os_get_thread_id() are happy with 0.
But the AML mutexes in exmutex.c expect a unique non-zero
number for each thread - as they track this thread_id
to permit the mutex re-entrancy defined by the ACPI spec.

http://bugzilla.kernel.org/show_bug.cgi?id=6687

Signed-off-by: Len Brown <len.brown@intel.com>
diff --git a/include/acpi/aclocal.h b/include/acpi/aclocal.h
index 56b8024..fbafee6 100644
--- a/include/acpi/aclocal.h
+++ b/include/acpi/aclocal.h
@@ -127,7 +127,7 @@
 
 /* This Thread ID means that the mutex is not in use (unlocked) */
 
-#define ACPI_MUTEX_NOT_ACQUIRED         (u32) -1
+#define ACPI_MUTEX_NOT_ACQUIRED         (acpi_thread_id) 0
 
 /* Table for the global mutexes */