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>
1 file changed