pkg-autotools: use $(HOST_DIR) instead of $(HOST_DIR)/usr as prefix

Remove the redundant usr/ component of the HOST_DIR paths. Since a
previous commit added a symlink from $(HOST_DIR)/usr to $(HOST_DIR),
everything keeps on working.

Build-tested with a bunch of autotools packages.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Reviewed-by: Romain Naour <romain.naour@smile.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/pkg-autotools.mk

@@ -220,7 +220,7 @@ define $(2)_CONFIGURE_CMDS
 	$$($$(PKG)_CONF_ENV) \
 	CONFIG_SITE=/dev/null \
 	./configure \
-		--prefix="$$(HOST_DIR)/usr" \
+		--prefix="$$(HOST_DIR)" \
 		--sysconfdir="$$(HOST_DIR)/etc" \
 		--localstatedir="$$(HOST_DIR)/var" \
 		--enable-shared --disable-static \