powerpc/tm: Fix comment

Update to real function name.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/tm.S

@@ -313,7 +313,7 @@ dont_backup_fp:
 	blr
 
 
-	/* void tm_recheckpoint(struct thread_struct *thread,
+	/* void __tm_recheckpoint(struct thread_struct *thread,
 	 *			  unsigned long orig_msr)
 	 *	- Restore the checkpointed register state saved by tm_reclaim
 	 *	  when we switch_to a process.