qcacmn: Avoid checking extcaps byte if equal to IE len

Reading extcaps from the scan entry currently checks if the byte
to be accessed is less than the length of the IE. Following this,
it will attempt to access the extcap IE using the requested byte
as the index.

Avoid accessing the extcap IE if the byte is greater than one less
than the ie_len (since indexing starts from zero).

CRs-Fixed: 2856212
Change-Id: Ie357edcd6095570c05871af657381c287e92504e