docs/gcov: Convert two tags to ref in dev-tools/gov.rst

Htmldocs does not display the chapter number, convert the two manual
chapter number tags to ref tags.
Signed-off-by: Wu XiangCheng <bobwxc@email.cn>
Acked-by: Peter Oberparleiter <oberpar@linux.ibm.com>
Link: https://lore.kernel.org/r/20210403113752.GA32236@mipcSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/gcov.rst

@@ -124,6 +124,8 @@ box for setups where kernels are built and run on the same machine. In
 cases where the kernel runs on a separate machine, special preparations
 must be made, depending on where the gcov tool is used:
 
+.. _gcov-test:
+
 a) gcov is run on the TEST machine
 
     The gcov tool version on the test machine must be compatible with the
@@ -143,6 +145,8 @@ a) gcov is run on the TEST machine
     machine. If any of the path components is symbolic link, the actual
     directory needs to be used instead (due to make's CURDIR handling).
 
+.. _gcov-build:
+
 b) gcov is run on the BUILD machine
 
     The following files need to be copied after each test case from test
@@ -211,7 +215,7 @@ Appendix A: gather_on_build.sh
 ------------------------------
 
 Sample script to gather coverage meta files on the build machine
-(see 6a):
+(see :ref:`Separated build and test machines a. <gcov-test>`):
 
 .. code-block:: sh
 
@@ -244,7 +248,7 @@ Appendix B: gather_on_test.sh
 -----------------------------
 
 Sample script to gather coverage data files on the test machine
-(see 6b):
+(see :ref:`Separated build and test machines b. <gcov-build>`):
 
 .. code-block:: sh