ARM: Keystone: No need to preserve r12 across smc call

Register r12 is caller-save, so no need preserve it keystone_cpu_smc().
Reported-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>

arch/arm/mach-keystone/smc.S

@@ -22,8 +22,8 @@
  * Return: Non zero value on failure
  */
 ENTRY(keystone_cpu_smc)
-	stmfd   sp!, {r4-r12, lr}
+	stmfd   sp!, {r4-r11, lr}
 	smc	#0
 	dsb
-	ldmfd   sp!, {r4-r12, pc}
+	ldmfd   sp!, {r4-r11, pc}
 ENDPROC(keystone_cpu_smc)