x86/um/vdso: Fix prototype of clock_gettime()

x86/um/vdso: Fix prototype of clock_gettime()

The clock_gettime() system call takes a pointer to
'struct __kernel_timespec', not 'struct __kernel_old_timespec'.
Right now this is not an issue as the vDSO never works with the
actual struct but only passes it through to the kernel.

Fix the prototype for consistency with the system call.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Link: https://patch.msgid.link/20251013-uml-vdso-cleanup-v1-1-a079c7adcc69@weissschuh.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>