fix build for pio/onewire/onewire_library (#374)

I think CMake `target_sources()` requires the keyword (INTERFACE |
 PUBLIC | PRIVATE)

Co-authored-by: mjcross <admin@crossleys.biz>

pio/CMakeLists.txt

@@ -9,6 +9,7 @@ if (NOT PICO_NO_HARDWARE)
     add_subdirectory(ir_nec)
     add_subdirectory(logic_analyser)
     add_subdirectory(manchester_encoding)
+    add_subdirectory(onewire)
     add_subdirectory(pio_blink)
     add_subdirectory(pwm)
     add_subdirectory(quadrature_encoder)

pio/onewire/onewire_library/CMakeLists.txt

@@ -1,5 +1,5 @@
 add_library(onewire_library INTERFACE)
-target_sources(onewire_library onewire_library.c)
+target_sources(onewire_library INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/onewire_library.c)
 
 # invoke pio_asm to assemble the state machine programs
 #