[gdb/testsuite] Fix duplicates in gdb.opt/inline-cmds.exp

With test-case gdb.opt/inline-cmds.exp on ppc64le-linux, I ran into:
...
PASS: gdb.opt/inline-cmds.exp: finish from marker
 ...
PASS: gdb.opt/inline-cmds.exp: finish from marker
DUPLICATE: gdb.opt/inline-cmds.exp: finish from marker
...

Fix this by issuing less passes.

Tested on ppc64le-linux.