rockchip: spi: the symbol for Hertz is Hz

fix typo

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>

drivers/spi/rk_spi.c

@@ -94,7 +94,7 @@ static void rkspi_set_clk(struct rockchip_spi_priv *priv, uint speed)
 	 */
 	if (clk_div > 0xfffe) {
 		clk_div = 0xfffe;
-		debug("%s: can't divide down to %d hz (actual will be %d hz)\n",
+		debug("%s: can't divide down to %d Hz (actual will be %d Hz)\n",
 		      __func__, speed, priv->input_rate / clk_div);
 	}