max_m5: add pointer validity check

- add validity check before dereference pointer
- fix wrongly register ->regmap_nvram.regmap if ->gauge_type = -1

Bug: 348083431
Test: build PASS, no kernel panic
Change-Id: Iee0dafec1a7e6286419056742075a6375e75cca0
Merged-In: I58b14f983cff0ea8e693c5551f99876927d3885d
Signed-off-by: Spade Lee <[email protected]>
2 files changed