ta: os_test: Silence unused parameter warning

Fixes following warning:

  | os_test.c: In function 'get_binblock_property':
  | os_test.c:72:12: warning: unused parameter 'nbuf' [-Wunused-parameter]
  |    72 |      char *nbuf, char **bbuf, size_t *bblen)
  |       |      ~~~~~~^~~~

Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Jerome Forissier <jerome@forissier.org>
Signed-off-by: Vesa Jääskeläinen <vesa.jaaskelainen@vaisala.com>
diff --git a/ta/os_test/os_test.c b/ta/os_test/os_test.c
index 9ffbdea..cfe3590 100644
--- a/ta/os_test/os_test.c
+++ b/ta/os_test/os_test.c
@@ -69,7 +69,7 @@
 }
 
 static TEE_Result get_binblock_property(TEE_PropSetHandle h,
-					char *nbuf, char **bbuf, size_t *bblen)
+					char *nbuf __unused, char **bbuf, size_t *bblen)
 {
 	TEE_Result res = TEE_ERROR_GENERIC;
 	uint32_t block_len = 0;