x86/speculation: Add cpu_show_gds() prototype

mainline inclusion
from mainline-v6.5-rc6
commit a57c27c7
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I7U9J3

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a57c27c7ad85c420b7de44c6ee56692d51709dda



---------------------------

The newly added function has two definitions but no prototypes:

drivers/base/cpu.c:605:16: error: no previous prototype for 'cpu_show_gds' [-Werror=missing-prototypes]

Add a declaration next to the other ones for this file to avoid the
warning.

Fixes: 8974eb58 ("x86/speculation: Add Gather Data Sampling mitigation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Tested-by: Daniel Sneddon <daniel.sneddon@linux.intel.com>
Cc: stable@kernel.org
Link: https://lore.kernel.org/all/20230809130530.1913368-1-arnd%40kernel.org


Signed-off-by: Zeng Heng <zengheng4@huawei.com>