[lldb] Fix TestFormattersSBAPI test

Summary:
This test was broken in two ways:
* Using the wrong API (e.g.: format = instead of SetFormat)
* The hex checker was only checking "01" which will pass with 0x0000001

Reviewers: clayborg, lanza, wallace

Reviewed By: clayborg

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D70884