usb: host: xhci-tegra: set MODULE_FIRMWARE for tegra186

Set the MODULE_FIRMWARE for tegra186, it's registered for 124/210 and
ensures the firmware is available at the appropriate time such as in
the initrd, else if the firmware is unavailable the driver fails with
the following errors:

tegra-xusb 3530000.usb: Direct firmware load for nvidia/tegra186/xusb.bin failed with error -2
tegra-xusb 3530000.usb: failed to request firmware: -2
tegra-xusb 3530000.usb: failed to load firmware: -2
tegra-xusb: probe of 3530000.usb failed with error -2

Fixes: 5f9be5f3 ("usb: host: xhci-tegra: Add Tegra186 XUSB support")
Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200120141910.116097-1-pbrobinson@gmail.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/xhci-tegra.c

@@ -1744,6 +1744,7 @@ MODULE_FIRMWARE("nvidia/tegra210/xusb.bin");
 
 static const char * const tegra186_supply_names[] = {
 };
+MODULE_FIRMWARE("nvidia/tegra186/xusb.bin");
 
 static const struct tegra_xusb_phy_type tegra186_phy_types[] = {
 	{ .name = "usb3", .num = 3, },