pcie: host: tegra: fix port register access

pcie: host: tegra: fix port register access

access root port registers only if rootport is active

Bug 1705758

Change-Id: Iac2f2b673d30824188220ddddf3a037535ab1f34
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Reviewed-on: http://git-master/r/837265
(cherry picked from commit be8e3f837be5cdf3ed8daec91ac0dedc29d0c7a7)
Reviewed-on: http://git-master/r/841724
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>