Fix spelling of 'reasonable' in comments

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/include/mbedtls/config.h b/include/mbedtls/config.h
index b0296eb..a1891bf 100644
--- a/include/mbedtls/config.h
+++ b/include/mbedtls/config.h
@@ -1493,7 +1493,7 @@
  * Enable an implementation of SHA-256 that has lower ROM footprint but also
  * lower performance.
  *
- * The default implementation is meant to be a reasonnable compromise between
+ * The default implementation is meant to be a reasonable compromise between
  * performance and size. This version optimizes more aggressively for size at
  * the expense of performance. Eg on Cortex-M4 it reduces the size of
  * mbedtls_sha256_process() from ~2KB to ~0.5KB for a performance hit of about