gdb fix PowerPC test gdb.arch/ppc-longdouble.exp

gdb fix PowerPC test gdb.arch/ppc-longdouble.exp

The test complains of duplicate tests.

DUPLICATE: gdb.arch/ppc-longdouble.exp: continue to breakpoint: return

The do_test calls gdb_continue_to_breakpoint "return".  The duplicates
are the result of calling do_test three times with different arguments.

This patch fixes the duplicate tests by adding $name to the
gdb_continue_to_breakpoint argument.

Patch tested on Power 10  ppc64le GNU/Linux, no duplicate tests reported,
no new regression errors.