[nrfconnect] Clear OTA image download offset (#19971)

The number of already downloaded bytes of an OTA image
was not cleared at the beginning of the OTA update.
As a result, if an OTA image transfer was interrupted, the
next attempt to download the image would fail.

Signed-off-by: Damian Krolik <damian.krolik@nordicsemi.no>

src/platform/nrfconnect/OTAImageProcessorImpl.cpp

@@ -46,6 +46,7 @@ CHIP_ERROR OTAImageProcessorImpl::PrepareDownload()
 CHIP_ERROR OTAImageProcessorImpl::PrepareDownloadImpl()
 {
     mHeaderParser.Init();
+    mParams = {};
     ReturnErrorOnFailure(System::MapErrorZephyr(dfu_target_mcuboot_set_buf(mBuffer, sizeof(mBuffer))));
     ReturnErrorOnFailure(System::MapErrorZephyr(dfu_multi_image_init(mBuffer, sizeof(mBuffer))));