Correct pluralisation errors in comments

Signed-off-by: Thomas Daubney <thomas.daubney@arm.com>
diff --git a/library/aes.c b/library/aes.c
index f615267..ae883b2 100644
--- a/library/aes.c
+++ b/library/aes.c
@@ -972,7 +972,7 @@
 #endif /* !MBEDTLS_AES_DECRYPT_ALT && !MBEDTLS_BLOCK_CIPHER_NO_DECRYPT */
 
 /*
- * Our intrinsics-based implementation of AESNI require the round keys to be
+ * Our intrinsics-based implementation of AESNI requires the round keys to be
  * aligned on a 16-byte boundary. We take care of this before creating them,
  * but the AES context may have moved (this can happen if the library is
  * called from a language with managed memory), and in later calls it might