mtd: nand: jz4740: fix '__iomem *' vs. '* __iomem'

The function jz_nand_ioremap_resource() needs a pointer to an __iomem
pointer as its last argument but this argument is declared as:
	void * __iomem *base

Fix this by using the correct declaration:
	void __iomem **base
which then also removes the following Sparse's warnings:
  282:15: warning: incorrect type in assignment (different address spaces)
  282:15:    expected void *[noderef] <asn:2>
  282:15:    got void [noderef] <asn:2> *
  322:57: warning: incorrect type in argument 4 (different address spaces)
  322:57:    expected void *[noderef] <asn:2> *base
  322:57:    got void [noderef] <asn:2> **
  402:67: warning: incorrect type in argument 4 (different address spaces)
  402:67:    expected void *[noderef] <asn:2> *base
  402:67:    got void [noderef] <asn:2> **

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>