Change GATT_ERROR to GATT_INVALID_PDU

GATT_ERROR occurs in bta_gattc_read_ext_prop_desc_cmpl when read
response is not 2 bytes. Thus changing to the correct status code
GATT_INVALID_PDU which describes this scenario.

Bug: 323309342
Test: m com.android.btservices
Flag: EXEMPT, no flow change
Change-Id: I623b2473ce841d2e289965f95b9c5ca8d29dd58a