devices/posix/epiphany:loader: Fix workgroup size calculation
devices/posix/epiphany:loader: Fix workgroup size calculation

Derive workgroup size from the team's device size, which is
P_TOPOLOGY_2D, instead from the team size, which is currently opened as
P_TOPOLOGY_FLAT by the e-hal pal backend.

Signed-off-by: Ola Jeppsson <793f970c52ded1276b9264c742f19d1888cbaf73@adapteva.com>

parallella/pal,aolofsson/pal,aolofsson/pal,aolofsson/pal,parallella/pal,parallella/pal,aolofsson/pal,parallella/pal,parallella/pal