Updating Tensorflow to 2.8.0

Change-Id: I12ac4f1bcfc7302deaa3b1074ea843e878641cce
diff --git a/requirements.txt b/requirements.txt
index 1f7f918..6f61d65 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
 ethos-u-vela
 pillow
 pyelftools
-tensorflow==2.7.0
+tensorflow==2.8.0