package/rtl8723bu: fix firmware install path

The rtl8723b_fw.bin file installed by this package is not actually used
by this driver at all. It is used by the btrtl Bluetooth driver in the
mainline kernel. The mainline btrtl driver looks for the file in
/lib/firmware/rtl_bt rather than /lib/firmware/rtlwifi. This driver's
Makefile has an install target that confirms the correct destination
firmware directory. It was like that since the very first version that
was added to Buildroot.

Signed-off-by: Doug Brown <doug@schmorgal.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/rtl8723bu/rtl8723bu.mk

@@ -13,7 +13,7 @@ RTL8723BU_MODULE_MAKE_OPTS = \
 	KSRC=$(LINUX_DIR)
 
 define RTL8723BU_INSTALL_TARGET_CMDS
-	$(INSTALL) -D -m 644 $(@D)/rtl8723b_fw.bin $(TARGET_DIR)/lib/firmware/rtlwifi/rtl8723b_fw.bin
+	$(INSTALL) -D -m 644 $(@D)/rtl8723b_fw.bin $(TARGET_DIR)/lib/firmware/rtl_bt/rtl8723b_fw.bin
 endef
 
 $(eval $(kernel-module))