auxdisplay: ht16k33: Fix refresh rate handling

Drop the call to msecs_to_jiffies(), as "HZ / fbdev->refresh_rate" is
already the number of jiffies to wait.

Fixes: 8992da44 ("auxdisplay: ht16k33: Driver for LED controller")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>