x86/tsc: Fix broken CONFIG_X86_TSC=n build

Add the missing return statement to the inline stub
tsc_store_and_check_tsc_adjust() and add the other stubs to make a
SMP=y,TSC=n build happy.

While at it, remove the unused variable from the UP variant of
tsc_store_and_check_tsc_adjust().

Fixes: commit ba75fb646931 ("x86/tsc: Sync test only for the first cpu in a package")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>