ACPICA: fix acpi_ex_release_mutex() comment

trivial, leftover from my NULL pointer dereference patch which got
'superseded' by commit fbc3be2

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/acpi/acpica/exmutex.c

@@ -375,8 +375,7 @@ acpi_ex_release_mutex(union acpi_operand_object *obj_desc,
 		return_ACPI_STATUS(AE_AML_MUTEX_NOT_ACQUIRED);
 	}
 
-	/* Must have a valid thread ID */
-
+	/* Must have a valid thread. */
 	if (!walk_state->thread) {
 		ACPI_ERROR((AE_INFO,
 			    "Cannot release Mutex [%4.4s], null thread info",