Corrected the help string of --force-block-config

Made the same correction in OPTIONS.md

Signed-off-by: Jacob Bohlin <jacob.bohlin@arm.com>
Change-Id: If79ee5c4c7464b40a72bbe6871b52a9eb0b308e1
diff --git a/ethosu/vela/vela.py b/ethosu/vela/vela.py
index 7271002..64a3381 100644
--- a/ethosu/vela/vela.py
+++ b/ethosu/vela/vela.py
@@ -294,7 +294,7 @@
         choices=[True, False],
         help="Controls the packing of multiple passes into a cascade (default: %(default)s)",
     )
-    parser.add_argument("--force-block-config", type=str, default="", help="Force a specific block configuration HxWxC")
+    parser.add_argument("--force-block-config", type=str, default="", help="Force a specific block configuration WxHxC")
     parser.add_argument("--timing", action="store_true", help="Time the compiler doing operations")
     parser.add_argument(
         "--accelerator-config",