octeontx2-pf: Drop the redundant preempt disable in __cn10k_aura_freeptr()

In order to fix a sleeping in atomic context bug, we have replaced the
per_cpu_ptr() with get_cpu_ptr() in commit 97b85312 ("octeontx2:
nic: Replace get_cpu()/put_cpu() with get_cpu_ptr()/put_cpu_ptr()")
to disable the preempt in __cn10k_aura_freeptr(). But
__cn10k_aura_freeptr() may be used in NAPI, the preempt disable seems
redundant. The commit 29e9c67b ("octeontx2-pf: Fix the use of
GFP_KERNEL in atomic context on rt") chose to add the get/put_cpu() in
cn10k_aura_freeptr(). With this change, the preempt disable in
__cn10k_aura_freeptr() becomes unnecessary. So restore the
per_cpu_ptr().

Signed-off-by: Kevin Hao <kexin.hao@windriver.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>