cpufreq: tegra: update comment for clarity

Tegra's driver got updated a bit (00917dd cpufreq: Tegra: implement intermediate
frequency callbacks) and implements new 'intermediate freq' infrastructure of
core. Above commit updated comments about when to call
clk_prepare_enable(pll_x_clk) and Doug wasn't satisfied with those comments and
said this:

> The "Though when target-freq is intermediate freq, we don't need to
> take this reference." makes me think that this function is actually
> called when target-freq is intermediate freq.  I don't think it is,
> right?

For better clarity just make that comment more explicit about when we call
tegra_target_intermediate().

Reviewed-by: Stephen Warren <[e-mail]>
Reported-and-reviewed-by: Doug Anderson <[e-mail]>
Signed-off-by: Viresh Kumar <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/tegra-cpufreq.c

···
 	/*
 	 * Take an extra reference to the main pll so it doesn't turn
 	 * off when we move the cpu off of it as enabling it again while we
-	 * switch to it from tegra_target() would take additional time. Though
-	 * when target-freq is intermediate freq, we don't need to take this
-	 * reference.
+	 * switch to it from tegra_target() would take additional time.
+	 *
+	 * When target-freq is equal to intermediate freq we don't need to
+	 * switch to an intermediate freq and so this routine isn't called.
+	 * Also, we wouldn't be using pll_x anymore and must not take extra
+	 * reference to it, as it can be disabled now to save some power.
 	 */
 	clk_prepare_enable(pll_x_clk);