devtool: sdk-update: fix not using updateserver config file option

devtool: sdk-update: fix not using updateserver config file option

We read the updateserver setting from the config file but we never
actually used that value - the code then went on to use only the value
supplied on the command line.

Fix courtesy of Dmitry Rozhkov <dmitry.rozhkov@intel.com>

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>