nand_base: sync flash detection functions with linux 3.9's code
this fix the problems introduced when detecting non ONFI flashes in
commit 4c2bdc8
"nand_base: detect more ONFI flash"
Signed-off-by: Eric Bénard <eric@eukrea.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>