fix(esp_hal_jpeg): initialize the includes variable

The cmakev2 build system may evaluate components recursively and all
components has to make sure all their variables are properly
initialized.

Fixes: a7115b6b36 ("refactor(jpeg): Split hal layer for jpeg")
Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

components/esp_hal_jpeg/CMakeLists.txt

@@ -3,6 +3,8 @@ if(${target} STREQUAL "linux")
     return() # This component is not supported by the POSIX/Linux simulator
 endif()
 
+set(includes)
+
 if(EXISTS "${CMAKE_CURRENT_LIST_DIR}/${target}/include")
     list(APPEND includes "${target}/include")
 endif()