[bsp][stm32l476-nucleo] change default RTT_DIR to ../..

bsp/stm32l476-nucleo/Kconfig

@@ -8,8 +8,8 @@ config $BSP_DIR
 config $RTT_DIR
     string
     option env="RTT_ROOT"
-    default: "rt-thread"
-    
+    default: "../.."
+
 # you can change the RTT_ROOT default: "rt-thread"
 # example : default "F:/git_repositories/rt-thread"
 
@@ -44,4 +44,4 @@ config BSP_USING_UART5
 config BSP_USING_LPUART1
     bool "using lpuart1"
     select RT_USING_SERIAL
-    default n
\ No newline at end of file
+    default n