dmaengine/amba-pl08x: No need to check "ch->signal < 0"

We have just executed following in pl08x_get_phy_channel():
	ch->signal = -1;

We don't have to compare "ch->signal < 0", as this will always be true.
Signed-off-by: Viresh Kumar <viresh.kumar@st.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/amba-pl08x.c

@@ -916,7 +916,7 @@ static int prep_phy_channel(struct pl08x_dma_chan *plchan,
 	 * need, but for slaves the physical signals may be muxed!
 	 * Can the platform allow us to use this channel?
 	 */
-	if (plchan->slave && ch->signal < 0 && pl08x->pd->get_signal) {
+	if (plchan->slave && pl08x->pd->get_signal) {
 		ret = pl08x->pd->get_signal(plchan);
 		if (ret < 0) {
 			dev_dbg(&pl08x->adev->dev,