imx-usb-loader: fix build issue

host-imx-usb-loader uses pkg-config to find libusb-1.0, but since it's
a host package, pkg-config needs to be passed the appropriate
environment variables, which are in $(HOST_CONFIGURE_OPTS). Therefore,
we now pass $(HOST_CONFIGURE_OPTS) in the environment when building
host-imx-usb-loader.

Fixes:

  http://autobuild.buildroot.org/results/fba/fba11afe003c512ed5c529c417f3a0feb920b0ed/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/imx-usb-loader/imx-usb-loader.mk

@@ -11,7 +11,7 @@ IMX_USB_LOADER_LICENSE_FILES = COPYING
 IMX_USB_LOADER_DEPENDENCIES = host-libusb
 
 define HOST_IMX_USB_LOADER_BUILD_CMDS
-	$(HOST_MAKE_ENV) $(MAKE) -C $(@D)
+	$(HOST_MAKE_ENV) $(HOST_CONFIGURE_OPTS) $(MAKE) -C $(@D)
 endef
 
 define HOST_IMX_USB_LOADER_INSTALL_CMDS