boot: main: avoid unused build warning

In case ESP32 SoC is used, *start will get
build warning as it is not used.

Signed-off-by: Sylvio Alves <sylvio.alves@espressif.com>

boot/zephyr/main.c

@@ -277,23 +277,23 @@ static void copy_img_to_SRAM(int slot, unsigned int hdr_offset)
  */
 static void do_boot(struct boot_rsp *rsp)
 {
-    void *start;
-
     BOOT_LOG_INF("br_image_off = 0x%x\n", rsp->br_image_off);
     BOOT_LOG_INF("ih_hdr_size = 0x%x\n", rsp->br_hdr->ih_hdr_size);
 
-#ifdef CONFIG_SOC_FAMILY_ESPRESSIF_ESP32
-    int slot = (rsp->br_image_off == IMAGE0_PRIMARY_START_ADDRESS) ?
-                PRIMARY_SLOT : SECONDARY_SLOT;
-    /* Load memory segments and start from entry point */
-    start_cpu0_image(IMAGE_INDEX_0, slot, rsp->br_hdr->ih_hdr_size);
-#else
+#ifndef CONFIG_SOC_FAMILY_ESPRESSIF_ESP32
+    void *start;
+
     /* Copy from the flash to HP SRAM */
     copy_img_to_SRAM(0, rsp->br_hdr->ih_hdr_size);
 
     /* Jump to entry point */
     start = (void *)(SRAM_BASE_ADDRESS + rsp->br_hdr->ih_hdr_size);
     ((void (*)(void))start)();
+#else
+    int slot = (rsp->br_image_off == IMAGE0_PRIMARY_START_ADDRESS) ?
+                PRIMARY_SLOT : SECONDARY_SLOT;
+    /* Load memory segments and start from entry point */
+    start_cpu0_image(IMAGE_INDEX_0, slot, rsp->br_hdr->ih_hdr_size);
 #endif /* CONFIG_SOC_FAMILY_ESPRESSIF_ESP32 */
 }