docs(porting): remove pull request terminology

The pull request terminology dates back from when TF-A repository was
hosted on Github. Use a terminology that is more suited to Gerrit
workflow.

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Change-Id: Ieecf47617ca1cdb76b9c4a83f63ba3c402b9e975
diff --git a/docs/getting_started/porting-guide.rst b/docs/getting_started/porting-guide.rst
index ae3ffb5..b9ccdb0 100644
--- a/docs/getting_started/porting-guide.rst
+++ b/docs/getting_started/porting-guide.rst
@@ -38,7 +38,7 @@
 source files in ``plat/arm/common/``. This is done so that there are no
 dependencies between platforms maintained by different people/companies. If you
 want to use any of the functionality present in ``plat/arm`` files, please
-create a pull request that moves the code to ``plat/common`` so that it can be
+propose a patch that moves the code to ``plat/common`` so that it can be
 discussed.
 
 Common modifications