serial: 8250_omap: Fix gpio check for auto RTS/CTS

serial: 8250_omap: Fix gpio check for auto RTS/CTS

There are two checks to see if the manual gpio is configured, but
these the check is seeing if the structure is NULL instead it
should check to see if there are CTS and/or RTS pins defined.

This patch uses checks for those individual pins instead of
checking for the structure itself to restore auto RTS/CTS.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Link: https://lore.kernel.org/r/20191006163314.23191-2-aford173@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>