fix(rmmd): fix bug, raised by coverity, when zeroing manifest struct

An "Incorrect expression (SIZEOF_MISMATCH)" bug was raised by coverity
on the memset for clearing the manifest structure. This patch resolves
that issue.

Signed-off-by: Harry Moulton <harry.moulton@arm.com>
Change-Id: I40431b972fc434d2b33f597813f22126d5d4cb70
diff --git a/services/std_svc/rmmd/rmmd_main.c b/services/std_svc/rmmd/rmmd_main.c
index a682e8e..033e868 100644
--- a/services/std_svc/rmmd/rmmd_main.c
+++ b/services/std_svc/rmmd/rmmd_main.c
@@ -234,7 +234,7 @@
 
 	/* Zero out and load the boot manifest at the beginning of the share area */
 	manifest = (struct rmm_manifest *)shared_buf_base;
-	memset((void *)manifest, 0, sizeof(manifest));
+	(void)memset((void *)manifest, 0, sizeof(struct rmm_manifest));
 
 	rc = plat_rmmd_load_manifest(manifest);
 	if (rc != 0) {