gitignore: add wildcard to match toplevel patch files

gitignore: add wildcard to match toplevel patch files

To support the basic workflow of trivial patches:

 git format-patch HEAD~.. ; git send-email --to foo@bar.com 0001-foo.patch

We don't want git status reporting on patches lying in the top
level dir in this case.

Cc: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>