mtd: nand: lpc32xx_slc: don't call nand_default_bbt directly

This driver is doing some strange logic here. If it doesn't have
flash-based BBT enabled, it allows nand_scan_tail() to scan the BBT. But
if it is using flash-based BBT, it tells nand_scan_tail() to skip
scanning, then it immediately calls the default BBT scanning function
itself.

As I read it, this logic is equivalent to the default nand_scan_tail()
behavior without interfering with NAND_SKIP_BBTSCAN or calling
nand_default_bbt() directly at all.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>