stm32/mboot: Fix fwupdate by replacing zlib with new deflate module.

Since commit 3533924c36 the zlib module has
been replaced by the new deflate module.  This commit updates the script
fwupdate.py to use the new deflate module.

Signed-off-by: Oliver Joos <oliver.joos@hispeed.ch>

ports/stm32/mboot/fwupdate.py

@@ -3,7 +3,7 @@
 
 from micropython import const
 import struct, time
-import zlib, machine, stm
+import deflate, machine, stm
 
 # Constants to be used with update_mpy
 VFS_FAT = 1
@@ -36,7 +36,7 @@ def dfu_read(filename):
     if hdr == b"Dfu":
         pass
     elif hdr == b"\x1f\x8b\x08":
-        f = zlib.DecompIO(f, 16 + 15)
+        f = deflate.DeflateIO(f, deflate.GZIP)
     else:
         print("Invalid firmware", filename)
         return None
@@ -231,7 +231,7 @@ def update_app_elements(
     # Check firmware is of .dfu or .dfu.gz type
     try:
         with open(filename, "rb") as f:
-            hdr = zlib.DecompIO(f, 16 + 15).read(6)
+            hdr = deflate.DeflateIO(f, deflate.GZIP).read(6)
     except Exception:
         with open(filename, "rb") as f:
             hdr = f.read(6)