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

Documentation/admin-guide/perf/imx-ddr.rst

@@ -43,7 +43,8 @@ value 1 for supported.
 
   AXI_ID and AXI_MASKING are mapped on DPCR1 register in performance counter.
   When non-masked bits are matching corresponding AXI_ID bits then counter is
-  incremented. Perf counter is incremented if
+  incremented. Perf counter is incremented if::
+
         AxID && AXI_MASKING == AXI_ID && AXI_MASKING
 
   This filter doesn't support filter different AXI ID for axid-read and axid-write