gdb/testsuite/rocm: fix rocm-multi-inferior-gpu.cpp

The gdb/testsuite/gdb.rocm/multi-inferior-gpu.cpp testcase contains a
call to execl which does not have NULL as a last argument.  This is
an invalid use of execl.  This patch fixes this oversight.

Change-Id: I03b60abe30468d71ba5089b240c6d00f9b8883b2
Approved-By: Tom Tromey <tom@tromey.com>
1 file changed