[C2F2] Fix CFI sanitizer issue in SystemStatusNetworkInfo

Make uint8_t variable int8_t to avoid potential
sub overflow.

Bug: 163454256
Test: build pass and verify basic function pass
CRs-fixed: 2756196
Change-Id: I1a660166f759616ce585f5c51a18df9d9a9d6bcb
1 file changed