arm64: delete dead code in this_cpu_set_vectors()

arm64: delete dead code in this_cpu_set_vectors()

The "slot" variable is an enum, and in this context it is an unsigned
int.  So the type means it can never be negative and also we never pass
invalid data to this function.  If something did pass invalid data then
this check would be insufficient protection.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/73859c9e-dea0-4764-bf01-7ae694fa2e37@kili.mountain
Signed-off-by: Will Deacon <will@kernel.org>