Fix article in documentation

Co-authored-by: Andrew Thoelke <andrew.thoelke@arm.com>
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/include/psa/crypto_values.h b/include/psa/crypto_values.h
index e80306c..7a41b22 100644
--- a/include/psa/crypto_values.h
+++ b/include/psa/crypto_values.h
@@ -672,7 +672,7 @@
 #define PSA_ALG_IS_AEAD(alg)                                            \
     (((alg) & PSA_ALG_CATEGORY_MASK) == PSA_ALG_CATEGORY_AEAD)
 
-/** Whether the specified algorithm is a asymmetric signature algorithm,
+/** Whether the specified algorithm is an asymmetric signature algorithm,
  * also known as public-key signature algorithm.
  *
  * \param alg An algorithm identifier (value of type #psa_algorithm_t).