kernel/sched: Fix double free on invalid isolcpus/nohz_full params

A previous patch left behind a redundant call to free_bootmem_cpumask_var
possibly leading to a double free (once in the if-branch and once in the
unwind code at the end of the function) if the isolcpus= or nohz_full=
kernel command line parameters failed validation, cf.:

https://lists.yoctoproject.org/g/linux-yocto/message/12797



Signed-off-by: Adrian Cinal <adriancinal1@gmail.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>