staging: sm750fb: use BIT macro for DE_STATE1 single-bit field

Replace complex definition of DE_STATE1 field and usage of FIELD_SET with
BIT() macro and open-coded register value modifications

Signed-off-by: Mike Rapoport <mike.rapoport@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>