docs: perf: imx-ddr.rst: get rid of a warning

    Documentation/admin-guide/perf/imx-ddr.rst:47: WARNING: Unexpected indentation.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/b27b54bd4f847032fd33313d6497ff320c0f3d78.1583250595.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>