qapi: Simplify QAPISchemaIfCond's interface for generating C

QAPISchemaIfCond.cgen() is only ever used like

    gen_if(ifcond.cgen())

and

    gen_endif(ifcond.cgen())

Simplify to

    ifcond.gen_if()

and

    ifcond.gen_endif()

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20210831123809.1107782-2-armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
[Import statements tidied up with isort]

scripts/qapi/schema.py

@@ -24,6 +24,8 @@ from .common import (
     c_name,
     cgen_ifcond,
     docgen_ifcond,
+    gen_endif,
+    gen_if,
 )
 from .error import QAPIError, QAPISemError, QAPISourceError
 from .expr import check_exprs
@@ -34,9 +36,15 @@ class QAPISchemaIfCond:
     def __init__(self, ifcond=None):
         self.ifcond = ifcond or {}
 
-    def cgen(self):
+    def _cgen(self):
         return cgen_ifcond(self.ifcond)
 
+    def gen_if(self):
+        return gen_if(self._cgen())
+
+    def gen_endif(self):
+        return gen_endif(self._cgen())
+
     def docgen(self):
         return docgen_ifcond(self.ifcond)