intel/perf: Fix mistake in description string

intel/perf: Fix mistake in description string

Along with fixing the grammar, this allows it to be deduplicated since
the properly worded description exists in later generations' XMLs.

Cuts 96 B from iris_dri.so and libvulkan_intel.so.

   text	   data	    bss	    dec	    hex	filename
 917613	      0	      0	 917613	  e006d	meson-generated_.._intel_perf_metrics.c.o (before)
 917511	      0	      0	 917511	  e0007	meson-generated_.._intel_perf_metrics.c.o (after)

   text	   data	    bss	    dec	    hex	filename
14131044 365708	 210004	14706756 e06844	iris_dri.so (before)
14130948 365708	 210004	14706660 e067e4	iris_dri.so (after)

   text	   data	    bss	    dec	    hex	filename
8124321	 214264	  22820	8361405	 7f95bd	libvulkan_intel.so (before)
8124225	 214264	  22820	8361309	 7f955d	libvulkan_intel.so (after)

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15237>