drm/amdgpu: fix topaz/tonga gmc assignment in 4.4 stable

BugLink: http://bugs.launchpad.net/bugs/1555640

When upstream commit 429c45de
was applied to 4.4 as d60703ca
it applied incorrectly to the tonga_ip_blocks array rather than
the topaz_ip_blocks array.  Fix that up here.

Bug:
https://bugzilla.kernel.org/show_bug.cgi?id=113951



Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>