PCI: endpoint: pci-epf-vntb: Fix the incorrect usage of __iomem attribute

PCI: endpoint: pci-epf-vntb: Fix the incorrect usage of __iomem attribute

__iomem attribute is supposed to be used only with variables holding the
MMIO pointer. But here, 'mw_addr' variable is just holding a 'void *'
returned by pci_epf_alloc_space(). So annotating it with __iomem is clearly
wrong. Hence, drop the attribute.

This also fixes the below sparse warning:

  drivers/pci/endpoint/functions/pci-epf-vntb.c:524:17: warning: incorrect type in assignment (different address spaces)
  drivers/pci/endpoint/functions/pci-epf-vntb.c:524:17:    expected void [noderef] __iomem *mw_addr
  drivers/pci/endpoint/functions/pci-epf-vntb.c:524:17:    got void *
  drivers/pci/endpoint/functions/pci-epf-vntb.c:530:21: warning: incorrect type in assignment (different address spaces)
  drivers/pci/endpoint/functions/pci-epf-vntb.c:530:21:    expected unsigned int [usertype] *epf_db
  drivers/pci/endpoint/functions/pci-epf-vntb.c:530:21:    got void [noderef] __iomem *mw_addr
  drivers/pci/endpoint/functions/pci-epf-vntb.c:542:38: warning: incorrect type in argument 2 (different address spaces)
  drivers/pci/endpoint/functions/pci-epf-vntb.c:542:38:    expected void *addr
  drivers/pci/endpoint/functions/pci-epf-vntb.c:542:38:    got void [noderef] __iomem *mw_addr

Fixes: e35f56bb0330 ("PCI: endpoint: Support NTB transfer between RC and EP")
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/20250709125022.22524-1-mani@kernel.org