generate_git: Fix check for existence of series file

$SERIES always contains at least the string "/series", so the check for
a zero-length string never triggers.

To fix this, check for the existence of the file instead.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
1 file changed