[SettingsProvider] change the log level of failed writes from WTF to E

Occasionally a super long setting was set in SettingsProvider (even though we already have a length restriction for most of the settings, sometimes the encoded setting length is still too long), which causes the serialization to fail when SettingsProvider writes it to disk. In that case, SettingProvider handles it gracefully by restoring to the old state and removing the invalid setting. Since this is an expected error that is already handled in the code, and is known to happen in the wild, change the log level from WTF from E.

Change-Id: I01b53888d183147772b1cf3de0bc2605f774f9ea
Test: na
BUG: 330914815