[][mt76-vendor: fix coverity errors]

[Description]
Fix coverity errors
- potential NP dereference
- memory leak after using strdup()

[Release-log]
N/A

Change-Id: I3f746c06cde6dbad34f8573106739c6af1f872f9
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5268154
1 file changed