xtensa: fix ATOMCTL register documentation

Make the WT entry match table 4-52 of the Xtensa ISA RM (RD-2012.5).
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

Documentation/xtensa/atomctl.txt

@@ -40,5 +40,5 @@ See Section 4.3.12.4 of ISA; Bits:
 ---------    ---------------         -----------------     ----------------
     0        Exception               Exception               Exception
     1        RCW Transaction         RCW Transaction         RCW Transaction
-    2        Internal Operation      Exception               Reserved
+    2        Internal Operation      Internal Operation      Reserved
     3        Reserved                Reserved                Reserved