freedreno/isaspec: Add missing dep of encode.py/decode.py calls on isa.py

Fixes: #5921
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14725>

src/compiler/isaspec/meson.build

@@ -22,3 +22,5 @@ prog_isaspec_decode = find_program('decode.py')
 idep_isaspec_decode = declare_dependency(sources : files('decode.c'), include_directories : include_directories('.'))
 
 prog_isaspec_encode = find_program('encode.py')
+
+isaspec_py_deps = files('isa.py')

src/freedreno/isa/meson.build

@@ -28,6 +28,7 @@ isa_depend_files = [
   'ir3-cat5.xml',
   'ir3-cat6.xml',
   'ir3-cat7.xml',
+  isaspec_py_deps
 ]
 
 ir3_isa = custom_target(