Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/b9904ca018d0
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #23390 from aosmond/bug1056173-3

Bug 1056173 -  [B2G][Camera][Gaia] Handle auto focus error callbacks, restore flash/focus modes correctly. r=justindarc

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https://hg.mozilla.org/integration/gaia-central/rev/d73600873d10
Author: Andrew Osmond <aosmond@gmail.com>
Desc: Bug 1056173 - Fix minor nits found by gaia-linter.

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https://hg.mozilla.org/integration/gaia-central/rev/6658cad1f12f
Author: Andrew Osmond <aosmond@gmail.com>
Desc: Bug 1056173 - Fix handling of auto focus errors, restoring of flash/focus. r=justindarc

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "0b9f4321cc0b35601a9cd287f9a423e9fa81c96a", 
+    "revision": "b9904ca018d00926f325b58be06b06828d29b3b6", 
     "repo_path": "/integration/gaia-central"
 }