[gdb/testsuite] Fix gdb.mi/gdb2549.exp with check-read1

[gdb/testsuite] Fix gdb.mi/gdb2549.exp with check-read1

When running gdb.mi/gdb2549.exp with check-read1, we get:
...
Running src/gdb/testsuite/gdb.mi/gdb2549.exp ...
FAIL: gdb.mi/gdb2549.exp: register values t (timeout)
...

The problem is that the command generates a lot of output, which is matched by
a single '.*':
...
mi_gdb_test "666-data-list-register-values t" \
  "666\\^done,register-values=\\\[\{number=\"$decimal\",value=\"$binary\"\}.*\\\]" \
  "register values t"
...

Fix this by splitting up the matching and calling exp_continue after each
number/value pair.

Tested on x86_64-linux with make targets check and check-read1.

gdb/testsuite/ChangeLog:

2020-03-03  Tom de Vries  <tdevries@suse.de>

	* gdb.mi/gdb2549.exp: Fix "register values t" check-read1 timeout.