msdk: set the right BRCParamMultiplier

BRCParamMultiplier in mfxInfoMFX is a parameter which specifies a
multiplier for bitrate control parameters [1], it impacts TargetKbps,
MaxKbps, BufferSizeInKB and InitialDelayInKB.

[1]: https://software.intel.com/en-us/node/628473
8 jobs for fix-bitrate in 41 minutes and 33 seconds (queued for 1 minute and 6 seconds)
Status Job ID Name Coverage
  Preparation
passed gst indent #78189

00:00:29

passed manifest #78188

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  Build
passed build fedora x86_64 #78190

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  Test
passed check fedora #78191

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  Full Builds
passed build android arm64 api28 #78192

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passed build cerbero cross win32 #78194

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passed build cerbero cross win64 #78195

00:16:23

passed build cerbero fedora x86_64 #78193

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