powerpc/prom: Simplify the logic to fetch SLB size

The code to fetch the SLB size from the device tree wants to first look
for "slb-size" and then if that's not found "ibm,slb-size".

We can simplify the code by looking for the properties and then if we
find one of them we set mmu_slb_size.

We also change the function name from check_cpu_slb_size() to
init_mmu_slb_size() as the function doesn't check anything, it only
initialises mmu_slb_size.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
[mpe: Rewrite change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/prom.c

@@ -218,22 +218,18 @@ static void __init check_cpu_pa_features(unsigned long node)
 }
 
 #ifdef CONFIG_PPC_STD_MMU_64
-static void __init check_cpu_slb_size(unsigned long node)
+static void __init init_mmu_slb_size(unsigned long node)
 {
 	const __be32 *slb_size_ptr;
 
-	slb_size_ptr = of_get_flat_dt_prop(node, "slb-size", NULL);
-	if (slb_size_ptr != NULL) {
-		mmu_slb_size = be32_to_cpup(slb_size_ptr);
-		return;
-	}
-	slb_size_ptr = of_get_flat_dt_prop(node, "ibm,slb-size", NULL);
-	if (slb_size_ptr != NULL) {
+	slb_size_ptr = of_get_flat_dt_prop(node, "slb-size", NULL) ? :
+			of_get_flat_dt_prop(node, "ibm,slb-size", NULL);
+
+	if (slb_size_ptr)
 		mmu_slb_size = be32_to_cpup(slb_size_ptr);
-	}
 }
 #else
-#define check_cpu_slb_size(node) do { } while(0)
+#define init_mmu_slb_size(node) do { } while(0)
 #endif
 
 static struct feature_property {
@@ -380,7 +376,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 
 	check_cpu_feature_properties(node);
 	check_cpu_pa_features(node);
-	check_cpu_slb_size(node);
+	init_mmu_slb_size(node);
 
 #ifdef CONFIG_PPC64
 	if (nthreads > 1)