x86/module: Remove unnecessary check in module_finalize()

The "calls" pointer can no longer be NULL after the following
commit:

   ab9fea59 ("x86/alternative: Simplify callthunk patching")

Delete this unnecessary check.

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/fcbb2f57-0714-4139-b441-8817365c16a1@stanley.mountain