staging:fbtft: Fix some warnings regarding types.

Running make C=1 M=drivers/staging/fbtft reports warnings about conversion
from __be16 to unsigned short. Change the type of the variables being
assigned into __be16 to remove those warnings.

Signed-off-by: Anthony Brandon <anthony@amarulasolutions.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>