powerpc/476: Fix sparse report

Fix sparse errors:
  arch/powerpc/platforms/44x/ppc476.c:236:17: warning: cast removes address space '__iomem' of expression
  arch/powerpc/platforms/44x/ppc476.c:241:34: warning: incorrect type in argument 1 (different address spaces)
  arch/powerpc/platforms/44x/ppc476.c:241:34:    expected void const volatile [noderef] __iomem *addr
  arch/powerpc/platforms/44x/ppc476.c:241:34:    got unsigned char [usertype] *
  arch/powerpc/platforms/44x/ppc476.c:243:17: warning: incorrect type in argument 1 (different address spaces)
  arch/powerpc/platforms/44x/ppc476.c:243:17:    expected void volatile [noderef] __iomem *addr
  arch/powerpc/platforms/44x/ppc476.c:243:17:    got unsigned char [usertype] *[assigned] fpga

Mark 'fpga' pointer as __iomem.

Fixes: ab9a4183 ("powerpc: Update currituck pci/usb fixup for new board revision")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/aa6055769b92a5d8685b8d0adab99c48a0b0ef4b.1631956926.git.christophe.leroy@csgroup.eu

arch/powerpc/platforms/44x/ppc476.c

@@ -219,7 +219,7 @@ static int board_rev = -1;
 static int __init ppc47x_get_board_rev(void)
 {
 	int reg;
-	u8 *fpga;
+	u8 __iomem *fpga;
 	struct device_node *np = NULL;
 
 	if (of_machine_is_compatible("ibm,currituck")) {
@@ -233,7 +233,7 @@ static int __init ppc47x_get_board_rev(void)
 	if (!np)
 		goto fail;
 
-	fpga = (u8 *) of_iomap(np, 0);
+	fpga = of_iomap(np, 0);
 	of_node_put(np);
 	if (!fpga)
 		goto fail;