serial: pl011: delete dangling bug flag

The bug flag .interrupt_may_hang is not used since commit
4fd0690b


"serial: pl011: implement workaround for CTS clear event issue"
so delete it.

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