When scalers are enabled, we need to program underrun
bubble counter to 0x50 to avoid Soft Pipe A underruns.
Make sure other bits dont get overwritten.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Cc: José Roberto de Souza <jose.souza@intel.com>
Signed-off-by: NAnusha Srivatsa <anusha.srivatsa@intel.com>
Signed-off-by: NClinton Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: NMatt Roper <matthew.d.roper@intel.com>
Reviewed-by: NClint Taylor <Clinton.A.Taylor@intel.com>
Signed-off-by: NLucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210519000625.3184321-17-lucas.demarchi@intel.com