[Intel-gfx] Fix one Macro definition in piglit

[Shuang He]

Just found a few tests under piglit/tests/shaders/ always complaint it 
can't find its program. It's due to a Macro definition is wrong in 
piglit CMakeList.txt.
Following patch seems fixes it:
diff --git a/tests/shaders/CMakeLists.txt b/tests/shaders/CMakeLists.txt
index 964fca1..398633c 100644
--- a/tests/shaders/CMakeLists.txt
+++ b/tests/shaders/CMakeLists.txt
@@ -21,7 +21,7 @@ link_libraries (
        ${GLEW_glew_LIBRARY}
 )

-add_definitions ( -DSOURCE_DIR="\\\"${piglit_SOURCE_DIR}/\\\"" )
+add_definitions ( -DSOURCE_DIR="${piglit_SOURCE_DIR}/" )

 add_executable (trinity-fp1 trinity-fp1.c)
 add_executable (fp-lit-mask fp-lit-mask.c)


Thanks
    --Shuang