spl, mtd, nand, atmel_nand: invert device ready pin logic

device ready pin is signalling that the device is ready on state 1
not on 0. Simmiliar as it is in drivers/mtd/nand/nand_spl_simple.c

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Andreas Bießmann <andreas.devel@googlemail.com>
Reviewed-by: Bo Shen <voice.shen@atmel.com>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Andreas Bießmann <andreas.devel@googlemail.com>