package/pkg-meson.mk: fix cross-compilation.conf

$$(STAGING_DIR) -> $(STAGING_DIR) in PKG_MESON_INSTALL_CROSS_CONF.

$$ resulted in `$(STAGING_DIR)` in the file instead of the expanded
value.

Note that this change only affects the etc config at:
host/etc/meson/cross-compilation.conf

Per-package cross-compilation.conf files are already correct.

Reviewed-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Gleb Mazovetskiy <glex.spb@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/pkg-meson.mk

@@ -193,7 +193,7 @@ define PKG_MESON_INSTALL_CROSS_CONF
 	    -e 's%@TARGET_LDFLAGS@%$(call make-comma-list,$(TARGET_LDFLAGS))@PKG_TARGET_CFLAGS@%g' \
 	    -e 's%@TARGET_CXXFLAGS@%$(call make-comma-list,$(TARGET_CXXFLAGS))@PKG_TARGET_CFLAGS@%g' \
 	    -e 's%@HOST_DIR@%$(HOST_DIR)%g' \
-	    -e 's%@STAGING_DIR@%$$(STAGING_DIR)%g' \
+	    -e 's%@STAGING_DIR@%$(STAGING_DIR)%g' \
 	    $(HOST_MESON_PKGDIR)/cross-compilation.conf.in \
 	    > $(HOST_DIR)/etc/meson/cross-compilation.conf.in
 	sed -e 's%@PKG_TARGET_CFLAGS@%%g' \