Use explicit constructor for QSslCertificate with value initialized argument

Previously the BluetoothDeviceLink::certificate() method was returning a
value initialized object which I believe default initializes the object.
However, Clang throws a build error at this because QSslCertificate has
explicit constructors. This change uses one of those constructors and
uses value intialization to default construct/initialize the argument
for it. It fixes the build and hopefully doesn't break anything since
this is a TODO anyways!

BUG: 469428



Signed-off-by: Ali Abdel-Qader <abdelqaderali@protonmail.com>
(cherry picked from commit bbac0aa0)