doc: Set correct syntax highlighting style

Several code blocks do not specify a language for syntax
highlighting. This results in Sphinx using a default highlighter
which is Python.

This patch adds the correct language to each code block that doesn't
already specify it.

Change-Id: Icce1949aabfdc11a334a42d49edf55fa673cddc3
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/security_advisories/security-advisory-tfv-3.rst b/docs/security_advisories/security-advisory-tfv-3.rst
index f74ef17..b395f13 100644
--- a/docs/security_advisories/security-advisory-tfv-3.rst
+++ b/docs/security_advisories/security-advisory-tfv-3.rst
@@ -68,7 +68,7 @@
   of the ``XN``, ``UXN`` or ``PXN`` bits in the translation tables. See the
   ``enable_mmu()`` function:
 
-  .. code:: c
+  ::
 
       sctlr = read_sctlr_el##_el();               \
       sctlr |= SCTLR_WXN_BIT | SCTLR_M_BIT;       \