flashrom_rpi_write: add size check before flashing

flashrom might do it anyways, but we have the read image and can
make sure the user didn't by accident provide the other image, for
example.

flashrom_rpi_write.sh

@@ -70,6 +70,7 @@ if [ ! "$have_chipname" -gt 0 ] ; then
 fi
 
 INPUT_IMAGE_NAME=$(basename ${INPUT_IMAGE_PATH})
+INPUT_IMAGE_SIZE=$(wc -c <"$INPUT_IMAGE_PATH")
 
 echo "verifying SPI connection by reading"
 TEMP_DIR=`mktemp -d`
@@ -84,6 +85,11 @@ if [ "$have_backupname" -gt 0 ] ; then
 	mv ${TEMP_DIR}/test1.rom ${BACKUPNAME}
 	echo "current image saved as ${BACKUPIMAGE}"
 fi
+TEMP_SIZE=$(wc -c <"$TEMP_DIR/test1.rom")
+if [ ! "$INPUT_IMAGE_SIZE" -eq "$TEMP_SIZE" ] ; then
+	echo "Error: read image (${TEMP_SIZE}) has different size that new image $INPUT_IMAGE_NAME (${INPUT_IMAGE_SIZE})"
+	exit 1
+fi
 rm -rf ${TEMP_DIR}
 
 echo -e "connection ok. flashing ${GREEN}${INPUT_IMAGE_NAME}${NC}"