msm: ep_pcie: Remove invalid return value

Enumeration can be called as part of handling PERST
interrupt as well as from probe function. Remove invalid
error value being returned and skip initialization of
PCIe resources if already done.

Change-Id: Idcae4fe98ccc06c98042b89060dae66018808f27
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>