gdb.base/default.exp: Change expected value for $_gdb_minor to 2.
    
    This change is needed, now that the version in gdb/version.in has
    been bumped from 9.1 to 9.2.
    
    gdb/testsuite/ChangeLog:
    
    	* gdb.base/default.exp: Change expected value for $_gdb_minor to 2.