powerpc: Remove redundant mflr in _switch

No need to execute mflr twice.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/entry_64.S

@@ -452,9 +452,7 @@ _GLOBAL(_switch)
 	/* r3-r13 are caller saved -- Cort */
 	SAVE_8GPRS(14, r1)
 	SAVE_10GPRS(22, r1)
-	mflr	r20		/* Return to switch caller */
-
-	std	r20,_NIP(r1)
+	std	r0,_NIP(r1)	/* Return to switch caller */
 	mfcr	r23
 	std	r23,_CCR(r1)
 	std	r1,KSP(r3)	/* Set old stack pointer */