clk: tegra: dfll: improve function-level documentation

Adjust variables to correspond to the names used in the parameter list of
the function.  Move the struct device * variable up to the place where it
appears in the parameter list.

Issue detected using Coccinelle (http://coccinelle.lip6.fr/

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Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>