mtd: nand: brcmnand: Zero bitflip is not an error

mtd: nand: brcmnand: Zero bitflip is not an error

A negative return value of brcmstb_nand_verify_erased_page() indicates a
real bitflip error of an erased page, and other return values (>= 0) show
the corrected bitflip number. Zero return value means no bitflip, but the
current driver code treats it as an error, and eventually leads to
falsely reported ECC error.

Fixes: 02b88eea9f9c ("mtd: brcmnand: Add check for erased page bitflip")
Signed-off-by: Albert Hsieh <[email protected]>
Acked-by: Boris Brezillon <[email protected]>
Signed-off-by: Richard Weinberger <[email protected]>