Cycles: Fix function inline attributes

forceinline attribute is only applicable for function which are
marked inline. Interestingly, it can be used for class methods
without explicit inline statement. But for functions it is another
story.

intern/cycles/kernel/kernels/cpu/kernel_cpu_image.h

@@ -37,7 +37,7 @@ namespace {
   } \
   (void)0
 
-ccl_always_inline float frac(float x, int *ix)
+ccl_device_inline float frac(float x, int *ix)
 {
   int i = float_to_int(x) - ((x < 0.0f) ? 1 : 0);
   *ix = i;