lint: exclude nvidia submodule from file list

From git's point of view submodules are a weird third thing between file
and directory. Avoid trying to apply file handling on a directory.

Change-Id: Ibbc9c28e1657d96413c5fb08705d30e25171254d
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/8372
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Tested-by: build bot (Jenkins)
1 file changed