spi/pl022: disable port when unused

commit fd316941cfee1fbd12746afea83720fb7823888a upstream.

Commit ffbbdd21329f3e15eeca6df2d4bc11c04d9d91c0
"spi: create a message queueing infrastructure"
Accidentally deleted the logic to disable the port
when unused leading to higher power consumption.
Fix this up.

Cc: Vinit Shenoy <vinit.shenoy@st.com>
Signed-off-by: Virupax Sadashivpetimath <virupax.sadashivpetimath@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>