x86/uml/syscalls: Remove array index from syscall initializers

The recent syscall table generator rework removed the index from the
initializers for native x86 syscall tables, but missed the UML syscall
tables.

Fixes: 44fe4895

 ("Stop filling syscall arrays with *_sys_ni_syscall")
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20210524181707.132844-2-brgerst@gmail.com