atmel_lcdfb: fix usage of CONTRAST_CTR in suspend/resume

An error was existing in the saving of CONTRAST_CTR register
across suspend/resume.

Signed-off-by: Hubert Feurstein <h.feurstein@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>