serial: omap: Remove the default setting of special character

Special character detect enable if enabled by default.Received data
comparison with XOFF2 data happens by default.

tty provides only XOFF1 no X0FF2 is provided so no need
to enable check for XOFF2.

Keeping this enabled might give some slow transfers due to dummy xoff2
comparison with xoff2 reset value.

Since not all want the XOFF2 support lets not enable it by
default.

Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>