powerpc/dt_cpu_ftrs: Make use of macro ISA_V3_0B

Macro ISA_V3_0B was defined but never used.  Use it instead of
literal.
Signed-off-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200610215114.167544-3-muriloo@linux.ibm.com

arch/powerpc/kernel/dt_cpu_ftrs.c

@@ -673,7 +673,7 @@ static void __init cpufeatures_setup_start(u32 isa)
 {
 	pr_info("setup for ISA %d\n", isa);
 
-	if (isa >= 3000) {
+	if (isa >= ISA_V3_0B) {
 		cur_cpu_spec->cpu_features |= CPU_FTR_ARCH_300;
 		cur_cpu_spec->cpu_user_features2 |= PPC_FEATURE2_ARCH_3_00;
 	}