Internalise functions flagged as internal

Signed-off-by: Thomas Daubney <thomas.daubney@arm.com>
diff --git a/tf-psa-crypto/drivers/builtin/src/sha1.c b/tf-psa-crypto/drivers/builtin/src/sha1.c
index b13381d..6c252f6 100644
--- a/tf-psa-crypto/drivers/builtin/src/sha1.c
+++ b/tf-psa-crypto/drivers/builtin/src/sha1.c
@@ -59,7 +59,7 @@
     return 0;
 }
 
-int mbedtls_internal_sha1_process(mbedtls_sha1_context *ctx,
+static int mbedtls_internal_sha1_process(mbedtls_sha1_context *ctx,
                                   const unsigned char data[64])
 {
     struct {