RISC-V: ACPI: Fix acpi_os_ioremap to return iomem address

acpi_os_ioremap() currently is a wrapper to memremap() on
RISC-V. But the callers of acpi_os_ioremap() expect it to
return __iomem address and hence sparse tool reports a new
warning. Fix this issue by type casting to  __iomem type.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202307230357.egcTAefj-lkp@intel.com/


Fixes: a91a9ffb ("RISC-V: Add support to build the ACPI core")
Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230724100346.1302937-1-sunilvl@ventanamicro.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>