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 #78189
gst indent

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passed #78188
manifest

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  Build
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build fedora x86_64

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  Test
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check fedora

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  Full Builds
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build android arm64 api28

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build cerbero cross win32

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build cerbero cross win64

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build cerbero fedora x86_64

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