[POWERPC] micro optimise pSeries_probe

We find the OF root the line before, we may as well use it.
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/platforms/pseries/setup.c

@@ -433,8 +433,8 @@ static int __init pSeries_probe_hypertas(unsigned long node,
 static int __init pSeries_probe(void)
 {
 	unsigned long root = of_get_flat_dt_root();
- 	char *dtype = of_get_flat_dt_prop(of_get_flat_dt_root(),
- 					  "device_type", NULL);
+ 	char *dtype = of_get_flat_dt_prop(root, "device_type", NULL);
+
  	if (dtype == NULL)
  		return 0;
  	if (strcmp(dtype, "chrp"))