arm64: zynqmp: fix preprocessor check for SPL_ZYNQMP_TWO_SDHCI

A missing CONFIG_ prefix while checking for this Kconfig variable makes the
check always fail. Fix it. While there also switch from the '#if defined'
form to the '#ifdef' form as the other checks in this function.

Fixes: 35e2b923 ("arm64: zynqmp: Fix logic around CONFIG_ZYNQ_SDHCI")
Signed-off-by: NLuca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: NMichal Simek <michal.simek@xilinx.com>

arch/arm/mach-zynqmp/spl.c

@@ -86,7 +86,7 @@ u32 spl_boot_device(void)
 	case SD_MODE1:
 	case SD1_LSHFT_MODE: /* not working on silicon v1 */
 /* if both controllers enabled, then these two are the second controller */
-#if defined(SPL_ZYNQMP_TWO_SDHCI)
+#ifdef CONFIG_SPL_ZYNQMP_TWO_SDHCI
 		return BOOT_DEVICE_MMC2;
 /* else, fall through, the one SDHCI controller that is enabled is number 1 */
 #endif