Bug 1573902 - Fix CDM Init return value name in IPDL. r=dminor

The return value for PChromiumCDM::Init was unused when the IPDL change was
first made. However, that quickly changed, but I failed to update the IPDL to
reflect that the value is now used to propagate the value that CDM interface 10
Widevine modules give us via the OnInitialized callback.

This patch fixes the IPDL to reflect that. The changes in C++ code have already
been made, so no change needed there.

Differential Revision: https://phabricator.services.mozilla.com/D41995

--HG--
extra : moz-landing-system : lando

dom/media/gmp/PChromiumCDM.ipdl

@@ -16,7 +16,7 @@ child:
 
   // cdm::ContentDecryptionModule9+10
   async Init(bool aAllowDistinctiveIdentifier,
-             bool aAllowPersistentState) returns (bool unused);
+             bool aAllowPersistentState) returns (bool aSuccess);
 
   async GetStatusForPolicy(uint32_t aPromiseId,
                            nsCString aMinHdcpVersion);