RootCanal: return the correct mode in Read Scan Enable

Fixes the PTS test GAP/DM/LEP/BV-05-C. Supposedly the PTS is
reading back the scan_enable value to apply bit changes
to it

Test: PTS test GAP/DM/LEP/BV-05-C
Bug: 245578454
Ignore-AOSP-First: cherry-pick from AOSP
Merged-In: I4bed5a6e47cb16001eb51c8ee51d365f2d85ed03
Change-Id: I4bed5a6e47cb16001eb51c8ee51d365f2d85ed03
(cherry picked from commit 5ba43fdc)