ACPI: CPPC: add __iomem annotation to generic_comm_base pointer

ppc_comm_addr is a virtual address to the PCC space and it's annotated
with __iomem. Therefore, generic_comm_base which gets assigned the value of
pcc_comm_address should be annotated as well.

This already happens in check_pcc_chan(), but not in send_pcc_cmd(), which
results in the following sparse warnings:

drivers/acpi/cppc_acpi.c:237:18: warning: cast removes address space '__iomem' of expression
drivers/acpi/cppc_acpi.c:299:9: warning: incorrect type in argument 2 (different address spaces)
drivers/acpi/cppc_acpi.c:299:9:    expected void volatile [noderef] __iomem *addr
drivers/acpi/cppc_acpi.c:299:9:    got unsigned short *
drivers/acpi/cppc_acpi.c:302:9: warning: incorrect type in argument 2 (different address spaces)
drivers/acpi/cppc_acpi.c:302:9:    expected void volatile [noderef] __iomem *addr
drivers/acpi/cppc_acpi.c:302:9:    got unsigned short *

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>