cdev: build & link fixes for NuttX protected build

- Always link to nuttx_fs for register/unregister_driver calls

Signed-off-by: Jukka Laitinen <jukkax@ssrc.tii.ae>

src/lib/cdev/CMakeLists.txt

@@ -51,6 +51,10 @@ px4_add_library(cdev
 )
 target_compile_options(cdev PRIVATE ${MAX_CUSTOM_OPT_LEVEL})
 
+if (${PX4_PLATFORM} STREQUAL "nuttx")
+	target_link_libraries(cdev PRIVATE nuttx_fs) # register/unregister driver
+endif()
+
 if(PX4_TESTING)
 	add_subdirectory(test)
 endif()