mtd: nand: lpc32xx_mlc: drop custom write_page callback

This driver doesn't need its own custom chip->write_page callback; the
only "custom" requirement is that this driver does not support subpage
writes, which we can avoid using the NAND_NO_SUBPAGE_WRITE flag. With
NAND_NO_SUBPAGE_WRITE, the default routine (nand_write_page()) should
perform the equivalent operations.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Roland Stigge <stigge@antcom.de>
Tested-by: Roland Stigge <stigge@antcom.de>