digsig: clean up whitespace in digsig.c

Clean up trailing whitespace in digsig.c.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>
digsig: overhaul dsi_sig_verify to use new APIs

Overhaul dsi_sig_verify to use new scatterlist crypto API.

Signed-off-by: Rupert Muchembled <rupert@rmuch.net>