ntb: intel: constify ioreadX() iomem argument (as in generic implementation)

The ioreadX() helpers have inconsistent interface. On some architectures
void *__iomem address argument is a pointer to const, on some not.

Implementations of ioreadX() do not modify the memory under the address so
they can be converted to a "const" version for const-safety and
consistency among architectures.

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Dave Jiang <[e-mail]>
Cc: Allen Hubbe <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Benjamin Herrenschmidt <[e-mail]>
Cc: "David S. Miller" <[e-mail]>
Cc: Geert Uytterhoeven <[e-mail]>
Cc: Helge Deller <[e-mail]>
Cc: Ivan Kokshaysky <[e-mail]>
Cc: Jakub Kicinski <[e-mail]>
Cc: "James E.J. Bottomley" <[e-mail]>
Cc: Jason Wang <[e-mail]>
Cc: Jon Mason <[e-mail]>
Cc: Kalle Valo <[e-mail]>
Cc: Matt Turner <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: "Michael S. Tsirkin" <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Richard Henderson <[e-mail]>
Cc: Rich Felker <[e-mail]>
Cc: Yoshinori Sato <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/ntb/hw/intel/ntb_hw_gen1.c

···
 			       ndev->peer_reg->spad);
 }
 
-static u64 xeon_db_ioread(void __iomem *mmio)
+static u64 xeon_db_ioread(const void __iomem *mmio)
 {
 	return (u64)ioread16(mmio);
 }

drivers/ntb/hw/intel/ntb_hw_gen3.h

···
 #define GEN3_DB_TOTAL_SHIFT		33
 #define GEN3_SPAD_COUNT			16
 
-static inline u64 gen3_db_ioread(void __iomem *mmio)
+static inline u64 gen3_db_ioread(const void __iomem *mmio)
 {
 	return ioread64(mmio);
 }

drivers/ntb/hw/intel/ntb_hw_intel.h

···
 struct intel_ntb_reg {
 	int (*poll_link)(struct intel_ntb_dev *ndev);
 	int (*link_is_up)(struct intel_ntb_dev *ndev);
-	u64 (*db_ioread)(void __iomem *mmio);
+	u64 (*db_ioread)(const void __iomem *mmio);
 	void (*db_iowrite)(u64 db_bits, void __iomem *mmio);
 	unsigned long			ntb_ctl;
 	resource_size_t			db_size;