The ssbi driver uses a busywait loop to read its status register.  Add
a comment explaining the timing of the device itself so that future
developers can better understand this delay, and possibly diagnose any
problems.
Signed-off-by: NDavid Brown <davidb@codeaurora.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>