[gdb/testsuite] Fix DUPLICATE in gdb.arch/pr25124.exp

With test-case gdb.arch/pr25124.exp, I run into:
...
PASS: gdb.arch/pr25124.exp: disassemble thumb instruction (1st try)
PASS: gdb.arch/pr25124.exp: disassemble thumb instruction (2nd try)
DUPLICATE: gdb.arch/pr25124.exp: disassemble thumb instruction (2nd try)
...

Fix this by using a comma instead of parentheses.

Tested on arm-linux.

Approved-By: Tom Tromey <tom@tromey.com>
1 file changed