Fix typos in C header files

Signed-off-by: Tobias Nießen <tniessen@tnie.de>
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/psa/crypto_compat.h b/include/psa/crypto_compat.h
index 5dabbd2..09ac488 100644
--- a/include/psa/crypto_compat.h
+++ b/include/psa/crypto_compat.h
@@ -44,7 +44,7 @@
 
 #define PSA_KEY_HANDLE_INIT MBEDTLS_SVC_KEY_ID_INIT
 
-/** Check wether an handle is null.
+/** Check whether an handle is null.
  *
  * \param handle  Handle
  *