drm/amd/powerplay: drop unneeded newline

PP_ASSERT_WITH_CODE prints a newline at the end of the message string,
so the message string does not need to include a newline explicitly.
Done using Coccinelle.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>