mtd: rawnand: brcmnand: Fixed incorrect sub-page ECC status

The brcmnand driver contains a bug in which if a page (example 2k byte)
is read from the parallel/ONFI NAND and within that page a subpage (512
byte) has correctable errors which is followed by a subpage with
uncorrectable errors, the page read will return the wrong status of
correctable (as opposed to the actual status of uncorrectable.)

The bug is in function brcmnand_read_by_pio where there is a check for
uncorrectable bits which will be preempted if a previous status for
correctable bits is detected.

The fix is to stop checking for bad bits only if we already have a bad
bits status.

Fixes: 27c5b17c

 ("mtd: nand: add NAND driver "library" for Broadcom STB NAND controller")
Signed-off-by: david regan <dregan@mail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/trinity-478e0c09-9134-40e8-8f8c-31c371225eda-1643237024774@3c-app-mailcom-lxa02