flash: return the amount of written bytes in flash_write0() and default_flash_copy()

source/core/flash.c

@@ -40,10 +40,10 @@ size_t default_flash_copy(struct flash_dev *dev, uint32_t dst, uint32_t src,
 		nbytes = min(sizeof data, len);
 
 		if (flash_read(dev, src, data, nbytes) == 0)
-			return -1;
+			return ret;
 
 		if (flash_write(dev, dst, data, nbytes) == 0)
-			return -1;
+			return ret;
 
 		dst += nbytes;
 		src += nbytes;
@@ -106,7 +106,7 @@ size_t flash_write0(struct flash_dev *dev, uint32_t addr, size_t len)
 		nbytes = min(sizeof data, len);
 
 		if (flash_write(dev, addr, data, nbytes) == 0)
-			return -1;
+			return ret;
 
 		addr += nbytes;
 		len -= nbytes;