omxvideodec: allocate as many input buffers as upstream in dynamic mode

Similar change as I just did for the encoder.
11 jobs for !41 with dynamic_mode_input_allocation_improvement in 13 minutes and 21 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Build Docker
passed alpine amd64 manifest builder docker #6656135

00:00:26

passed android docker #6656134

00:01:17

passed cerbero fedora amd64 docker #6656133

00:01:44

passed fedora amd64 docker #6656132

00:00:38

passed gst-indent amd64 docker #6656136

00:00:45

 
  Preparation
passed check allow-edit #6656143

00:00:11

passed gst indent #6656140

00:00:07

passed manifest #6656138
manual

00:00:18

 
  Build
passed build gst-omx tizonia fedora x86_64 #6656150

00:03:33

passed build gst-omx zynq fedora x86_64 #6656146

00:03:33

 
  Integrate
passed documentation #6656152

00:11:09