After fixing bug 68235, it appears the maximum memory speed (or core speed)
can't always be reached. This situation depends on the voltage tweaking seen on
some cards. As an exemple, XFX HD-695X-ZNDC has the following maximum values:
max_sclk_vddc->80000, max_mclk_vddci->125000, max_mclk_vddc->125000.
However, the maximum memory clock value should be 130000 and the core clock
should be 83000.

As Alex Deucher explained: "This patch set works around the issue by limiting
the sclk and mclk to the highest levels listed in the clk/voltage dependency
tables.  I'll need to dig a bit more internally to try and figure out how to
handle these clks properly."