spinand_mtd_regular_page_read() returns ret after iterating over the
requested pages. If the request contains no data or OOB bytes, the
iterator does not run and ret is not assigned. Initialize it to 0 for the
empty request path.
Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com> Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>