.gitignore: Add rule for *.patch

Ignore any patch files that we find, since these are likely to be
used when sending patches upstream.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: David Gibson <david@gibson.dropbear.id.au>

.gitignore

@@ -1,6 +1,7 @@
 *.o
 *.d
 *.a
+*.patch
 *.so
 *~
 *.tab.[ch]