AP_HAL_Linux: remove redundant ifdef

CONFIG_HAL_BOARD_SUBTYPE should be set in the boards header.

libraries/AP_HAL/board/linux.h

@@ -392,6 +392,7 @@
 #elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_RST_ZYNQ
 #define HAL_BOARD_LOG_DIRECTORY "/mnt/APM/logs"
 #define HAL_BOARD_TERRAIN_DIRECTORY "/mnt/APM/terrain"
+#define HAL_BOARD_STORAGE_DIRECTORY "/mnt/APM"
 #define HAL_INS_DEFAULT HAL_INS_RST
 #define HAL_INS_DEFAULT_G_ROTATION ROTATION_ROLL_180_YAW_90
 #define HAL_INS_DEFAULT_A_ROTATION ROTATION_ROLL_180_YAW_90

libraries/AP_HAL_Linux/Storage.cpp

@@ -22,8 +22,6 @@ using namespace Linux;
 // card for ArduCopter and ArduPlane
 #if APM_BUILD_TYPE(APM_BUILD_Replay)
 #define STORAGE_DIR "."
-#elif CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_RST_ZYNQ
-#define STORAGE_DIR "/mnt/APM"
 #else
 #define STORAGE_DIR HAL_BOARD_STORAGE_DIRECTORY
 #endif