phy: tegra: mark tegra_xusb_lane_lookup_function() static

We get 1 warning when building kernel with W=1:
drivers/phy/tegra/xusb.c:104:5: warning: no previous prototype for 'tegra_xusb_lane_lookup_function' [-Wmissing-prototypes]

In fact, this function is only used in the file in which it is
declared and don't need a declaration, but can be made static.
So this patch marks it 'static'.
Signed-off-by: NBaoyou Xie <baoyou.xie@linaro.org>
Acked-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NThierry Reding <treding@nvidia.com>
Signed-off-by: NKishon Vijay Abraham I <kishon@ti.com>

drivers/phy/tegra/xusb.c

@@ -102,7 +102,8 @@ tegra_xusb_pad_find_phy_node(struct tegra_xusb_pad *pad, unsigned int index)
 	return of_find_node_by_name(np, pad->soc->lanes[index].name);
 }
 
-int tegra_xusb_lane_lookup_function(struct tegra_xusb_lane *lane,
+static int
+tegra_xusb_lane_lookup_function(struct tegra_xusb_lane *lane,
 				    const char *function)
 {
 	unsigned int i;