I believe you can do this in a few ways. First, I am assuming you are passing in an array to the model function and that array is $filters
.
Option One
$this->db->select('*');
$this->db->from('tbl_admins');
$this->db->where('email', $filters["email"]);
$this->db->or_where('uname', $filters["email"]);
$this->db->where('upass', $filters["password"]);
Option Two
$this->db->select('*');
$this->db->from('tbl_admins');
$this->db->where("(email = '$filters["email"]' OR uname = '$filters["email"]') AND upass = '$filters["password"]'");
I did not test, so you may need to adjust the variables in option two's where a bit. But that is fairly close to what you want.
Here is another example of a similar Stack Overflow question.