[gdb/testsuite, tclint] Fix gdb.rocm

Running tclint on the test-cases in gdb.rocm shows a few problems:
...
precise-memory-multi-inferiors.exp:33:5: expected braced word or word \
  without substitutions in argument interpreted as expr [command-args]
precise-memory-multi-inferiors.exp:43:5: expected braced word or word \
  without substitutions in argument interpreted as expr [command-args]
precise-memory-multi-inferiors.exp:55:5: expected braced word or word \
  without substitutions in argument interpreted as expr [command-args]
...

Fix these.

The gdb.rocm test-cases are unsupported for me, so I can't test this.