hearing_aid: Potential OOB in reading the PSM handle

- invalid length check for len > 2 instead of < 2
- value is read with arch endianness instead of
  explicit little endian order

Bug: 331817295
Test: m com.android.btservices
Flag: EXEMPT, minor bugfix
Change-Id: Icd4ca8b99fbf288cfce19f4685476096011ddb2b