google_bms: fix idx size overflow

Bug: 333629531
Change-Id: I16f8b5259106b5f7dbfc7b16d896174d1a3fa206
Signed-off-by: Jenny Ho <hsiufangho@google.com>
(cherry picked from commit 11a05eccc1df6e819bc4290ec0b06c64253bafeb)
1 file changed