staging: rtl8723bs: Mark ACPI table declaration as used

Clang emits the following warning:

drivers/staging/rtl8723bs/os_dep/sdio_intf.c:25:36: warning: variable
'acpi_ids' is not needed and will not be emitted
[-Wunneeded-internal-declaration]
static const struct acpi_device_id acpi_ids[] = {
                                   ^
1 warning generated.

Mark acpi_ids with the attribute __used, which makes it clear to Clang
that we don't want this warning while not inhibiting Clang's dead code
elimination from removing the unreferenced internal symbol when moving
the data to the globally available symbol with MODULE_DEVICE_TABLE.

$ nm -S drivers/staging/rtl8723bs/os_dep/sdio_intf.o | grep acpi
0000000000000000 0000000000000040 R __mod_acpi__acpi_ids_device_table

Link: https://github.com/ClangBuiltLinux/linux/issues/169


Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>