[nrf noup] boot: bootutil: Fix issue with network core update persisting

nrf-squash! [nrf noup] boot: nrf53-specific customizations

Fixes an issue whereby network core updates would persist when
configured in update only mode and continually update on each
reboot

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

Author: nordicjm

boot/bootutil/src/loader.c

@@ -1516,13 +1516,14 @@ boot_validated_swap_type(struct boot_loader_state *state,
                 swap_type = BOOT_SWAP_TYPE_FAIL;
             } else {
                 BOOT_LOG_INF("Done updating network core");
-#if defined(MCUBOOT_SWAP_USING_SCRATCH) || defined(MCUBOOT_SWAP_USING_MOVE)
                 /* swap_erase_trailer_sectors is undefined if upgrade only
-                 * method is used. There is no need to erase sectors, because
-                 * the image cannot be reverted.
+                 * method is used
                  */
+#if defined(MCUBOOT_SWAP_USING_SCRATCH) || defined(MCUBOOT_SWAP_USING_MOVE)
                 rc = swap_erase_trailer_sectors(state,
                         secondary_fa);
+#elif defined(MCUBOOT_OVERWRITE_ONLY)
+                rc = flash_area_erase(secondary_fa, 0, flash_area_get_size(secondary_fa));
 #endif
                 swap_type = BOOT_SWAP_TYPE_NONE;
             }