cfg80211: mlme: Silently ignore duplicate management registrations

Instead of erroring out, just ignore the call

Change-Id: I5ff67100ea2d7f53bd30b6844c462bca71c24d15
Merge branch 'cm-11.0' of https://github.com/CyanogenMod/android_kernel_lge_msm8974 into cm-11.0