I am not sure why spi.h is still generating warnings.  A few more parentheses and that seems to fix the problem

In last changed to poll(),cConverted timeout to unsigned to eliminate the possibility of overflow of signed overflow.

vfs/poll: round timeout up to next full tick.  Calling poll() with timeout less than half tick (thus MSEC2TICK(timeout) => 0) caused returning error with EAGAIN. Instead of rounding timeout down, value should be rounded up. Open Group spec for poll says:  "Implementations may place limitations on the granularity of timeout intervals. If the requested timeout interval requires a finer granularity than the implementation supports, the actual timeout interval will be rounded up to the next supported value."