docs: trace-uses.rst: remove bogus c-domain tags

There are some c-domain tags that are wrong. While this won't
cause problems with Sphinx < 3.0, this cause troubles with
newer versions, as the C parser won't recognize the contents
of the tag, and will drop it from the output.

Let's just place them at literal blocks.
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

Documentation/trace/ftrace-uses.rst

@@ -55,17 +55,17 @@ an ftrace_ops with ftrace:
 
 Both .flags and .private are optional. Only .func is required.
 
-To enable tracing call:
+To enable tracing call::
 
-.. c:function::  register_ftrace_function(&ops);
+    register_ftrace_function(&ops);
 
-To disable tracing call:
+To disable tracing call::
 
-.. c:function::  unregister_ftrace_function(&ops);
+    unregister_ftrace_function(&ops);
 
-The above is defined by including the header:
+The above is defined by including the header::
 
-.. c:function:: #include <linux/ftrace.h>
+    #include <linux/ftrace.h>
 
 The registered callback will start being called some time after the
 register_ftrace_function() is called and before it returns. The exact time