linux-phytec-ti

mtd: spi-nor: add forward declaration for mtd_info

This header can't actually stand alone, as it relies on the declaration
(but not definition) of struct mtd_info. Let's fix that.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>