dfu: newline after updating

Currently output of dfu commands ends on a line with leading hash signs
('#'). The succeeding output should be placed on a new line.

After writing updates via dfu print a new line.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>