gdb.ada/minsyms.exp: Don't hardcode the variable's address

gdb.ada/minsyms.exp: Don't hardcode the variable's address

This new testcase has a test that fails like this here:

  $1 = (<data variable, no debug info> *) 0x60208c <some_minsym>
  (gdb) FAIL: gdb.ada/minsyms.exp: print &some_minsym

The problem is that the testcase hardcodes an expected address for the
"some_minsym" variable, which obviously isn't stable.

Fix that by expecting $hex instead.

gdb/testsuite/ChangeLog:
2017-11-21  Pedro Alves  <palves@redhat.com>

	* gdb.ada/minsyms.exp: Accept any address for 'some_minsym'.