V4L/DVB (3300b): .gitignore should also ignore StGit generated dirs

StGit genreates patches-* when you run stg export command.
It makes no sense to show such directories as changes on git status.
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>

.gitignore

@@ -30,3 +30,5 @@ include/linux/autoconf.h
 include/linux/compile.h
 include/linux/version.h
 
+# stgit generated dirs
+patches-*