powerpc/40x: Clear MSR_DR in one insn instead of two

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/misc_32.S

@@ -244,8 +244,7 @@ _GLOBAL(_nmask_and_or_msr)
  */
 _GLOBAL(real_readb)
 	mfmsr	r7
-	ori	r0,r7,MSR_DR
-	xori	r0,r0,MSR_DR
+	rlwinm	r0,r7,0,~MSR_DR
 	sync
 	mtmsr	r0
 	sync
@@ -262,8 +261,7 @@ _GLOBAL(real_readb)
  */
 _GLOBAL(real_writeb)
 	mfmsr	r7
-	ori	r0,r7,MSR_DR
-	xori	r0,r0,MSR_DR
+	rlwinm	r0,r7,0,~MSR_DR
 	sync
 	mtmsr	r0
 	sync