ARM: rmobile: Convert ifdef in rmobile_get_prr() to IS_ENABLED()

Switch ifdef in rmobile_get_prr() to IS_ENABLED() macro.
The CONFIG_RCAR_GEN3 will never have SPL counterpart, so
the IS_ENABLED() macro is the right one here. No functional
change, except for improved build test coverage.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>

arch/arm/mach-rmobile/cpu_info-rcar.c

@@ -14,11 +14,10 @@
 
 static u32 rmobile_get_prr(void)
 {
-#ifdef CONFIG_RCAR_GEN3
-	return readl(0xFFF00044);
-#else
+	if (IS_ENABLED(CONFIG_RCAR_GEN3))
+		return readl(0xFFF00044);
+
 	return readl(0xFF000044);
-#endif
 }
 
 u32 rmobile_get_cpu_type(void)