rockchip: rk3399: fix incorrect ifdef check on SPL_DM_REGULATOR

The check to perform is on CONFIG_SPL_DM_REGULATOR and not
SPL_DM_REGULATOR. Also switch to in-code check instead of ifdefs.

Fixes: 07586ee4322a ("rockchip: rk3399: Support common spl_board_init")
Cc: Quentin Schulz <foss+uboot@0leil.net>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Peter Robinson <pbrobinson@gmail.com>
Tested-by: Peter Robinson <pbrobinson@gmail.com> # Rock960
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/rk3399/rk3399.c b/arch/arm/mach-rockchip/rk3399/rk3399.c
index 21db03b..572c843 100644
--- a/arch/arm/mach-rockchip/rk3399/rk3399.c
+++ b/arch/arm/mach-rockchip/rk3399/rk3399.c
@@ -275,13 +275,14 @@
 		rk3399_force_power_on_reset();
 #endif
 
-#if defined(SPL_DM_REGULATOR)
-	/*
-	 * Turning the eMMC and SPI back on (if disabled via the Qseven
-	 * BIOS_ENABLE) signal is done through a always-on regulator).
-	 */
-	if (regulators_enable_boot_on(false))
-		debug("%s: Cannot enable boot on regulator\n", __func__);
-#endif
+	if (IS_ENABLED(CONFIG_SPL_DM_REGULATOR)) {
+		/*
+		 * Turning the eMMC and SPI back on (if disabled via the Qseven
+		 * BIOS_ENABLE) signal is done through a always-on regulator).
+		 */
+		if (regulators_enable_boot_on(false))
+			debug("%s: Cannot enable boot on regulator\n",
+			      __func__);
+	}
 }
 #endif