mtd: change the location of the ONFI detected log

Some strange nand chip(such as Hynix H27UBG8T2A) can pass the `ONFI` signature
check. So the log can be printed out even it is not an ONFI nand indeed.

Change this log to the end of the function. Print out the log only when we
really detect an ONFI nand.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Acked-by: Florian Fainelli <ffainelli@freebox.fr>
Acked-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>