serial: bfin-uart: remove redundant CTS check for hardware CTS control.

Blackfin hardware CTS control generate interrupt for both CTS on and off.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>