Fix custom_target breakage

The recent meson format commit reordered arguments of some
custom_target calls, where the code expected the first input to be the
script being run.  Hardcode that argument instead.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I2d895da8ad2ddb0aba3a545129ff698438f8eaa7
diff --git a/presence/meson.build b/presence/meson.build
index 11db05a..e8f5476 100644
--- a/presence/meson.build
+++ b/presence/meson.build
@@ -26,10 +26,11 @@
 
 # Only needed for YAML config
 if get_option('json-config').disabled()
+    script = files('pfpgen.py')
     generated_hpp_dep = custom_target(
         'generated.hpp',
-        input: files(conf.get_unquoted('PRESENCE_YAML_FILE'), './pfpgen.py'),
-        command: [python_prog, '@INPUT0@', 'generate-cpp', '-i', '@INPUT1@'],
+        input: files(conf.get_unquoted('PRESENCE_YAML_FILE')),
+        command: [python_prog, script, 'generate-cpp', '-i', '@INPUT0@'],
         capture: true,
         output: 'generated.hpp',
     )