meson: set correct install path for gdb helper
The original version of the patch used glib-2.0 but that was later changed to gstreamer-1.0 for autotools. The meson file was forgotten.
Fix the path to match the one used in libgstreamer-gdb.py.in.
The original version of the patch used glib-2.0 but that was later changed to gstreamer-1.0 for autotools. The meson file was forgotten.
Fix the path to match the one used in libgstreamer-gdb.py.in.