Since commit 4fd0690b
"serial: pl011: implement workaround for CTS clear event issue"
the PL011 UART is no longer at risk to hang up, so get rid
of the callback altogether.

Cc: Rajanikanth H.V <rajanikanth.hv@stericsson.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Acked-by: NLee Jones <lee.jones@linaro.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>