mfd: omap-usb: prepare/unprepare clock while enable/disable

This should fix the following warning at boot on OMAP5 uEVM
[    8.783155] WARNING: CPU: 0 PID: 1 at drivers/clk/clk.c:883 __clk_enable+0x94/0xa4()

Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/omap-usb-tll.c

@@ -429,7 +429,7 @@ int omap_tll_enable(struct usbhs_omap_platform_data *pdata)
 			if (IS_ERR(tll->ch_clk[i]))
 				continue;
 
-			r = clk_enable(tll->ch_clk[i]);
+			r = clk_prepare_enable(tll->ch_clk[i]);
 			if (r) {
 				dev_err(tll_dev,
 				 "Error enabling ch %d clock: %d\n", i, r);
@@ -460,7 +460,7 @@ int omap_tll_disable(struct usbhs_omap_platform_data *pdata)
 	for (i = 0; i < tll->nch; i++) {
 		if (omap_usb_mode_needs_tll(pdata->port_mode[i])) {
 			if (!IS_ERR(tll->ch_clk[i]))
-				clk_disable(tll->ch_clk[i]);
+				clk_disable_unprepare(tll->ch_clk[i]);
 		}
 	}