doc: Fix indentation in build options documentation

Sphinx was showing the following warning message:

docs/getting_started/build-options.rst:200: WARNING: Bullet list ends
without a blank line; unexpected unindent.

Change-Id: Iad5d49c1e0d25dd623ad15bce1af31babf860c03
Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>

docs/getting_started/build-options.rst

@@ -196,7 +196,7 @@ Common build options
    builds, but this behaviour can be overridden in each platform's Makefile or
    in the build command line.
 
- -  ``ENABLE_LTO``: Boolean option to enable Link Time Optimization (LTO)
+-  ``ENABLE_LTO``: Boolean option to enable Link Time Optimization (LTO)
    support in GCC for TF-A. This option is currently only supported for
    AArch64. Default is 0.