staging: dgap: Fix trailing whitespace in digi.h

This patch fixed trailing whitespace error found by
checkpatch.pl in dgap/digi.h

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Lidza Louina <Lidza.Louina@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>