or if the next message on
the queue (which is not the actual next message, as the pump
message has removed the next message from the queue) is not for
the same SPI device as that Of the previous one, giveback will
de-activate the chip select activated by pump_message(),
which is wrong.

To solve this problem pump_message is made not to run and
access the queue until the giveback is done handling the queue.
I.e. by making the cur_msg NULL after the giveback has read the
queue.

Also a state variable has been introduced to keep track of when
the CS for next message is already activated and avoid to
double-activate it.

Reviewed-by: Viresh Kumar <viresh.kumar@st.com>
Signed-off-by: Virupax Sadashivpetimath <virupax.sadashivpetimath@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>