sparc: vdso: Disable UBSAN instrumentation

The UBSAN instrumentation cannot work in the vDSO since it is executing
in userspace, so disable it in the Makefile. Fixes the build failures
such as:

arch/sparc/vdso/vclock_gettime.c:217: undefined reference to `__ubsan_handle_shift_out_of_bounds'

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://lore.kernel.org/all/20240224073617.GA2959352@ravnborg.org


Signed-off-by: Kees Cook <keescook@chromium.org>