doc: Fix broken code blocks in coding guidelines

Sections 2.2, 2.3 and 2.4 contained example code blocks that were not
being formatted properly due to missing newlines.

Change-Id: I0dbce90c931cf69e4f47d2ccbcc8bc0e20f8fd66
Signed-off-by: Paul Beesley <paul.beesley@arm.com>
diff --git a/docs/coding-guidelines.rst b/docs/coding-guidelines.rst
index 5a30e91..d5ac978 100644
--- a/docs/coding-guidelines.rst
+++ b/docs/coding-guidelines.rst
@@ -72,6 +72,7 @@
 
 The example below illustrates the ordering rules using some contrived header
 file names; this type of name reuse should be otherwise avoided.
+
 .. code:: c
 
   #include <string.h>
@@ -98,6 +99,7 @@
 is including them, use the ``<...>`` variant.
 
 Example (bl1_fwu.c):
+
 .. code:: c
 
   #include <assert.h>
@@ -114,6 +116,7 @@
 particular for the file ``platform_def.h``.
 
 Example:
+
 .. code:: c
 
   PLAT_INCLUDES  += -Iinclude/plat/myplat/include