gallium/winsys/kms: Fix dumb buffer bpp

The bpp in the dumb buffer creation request is hardcoded to 32, which is an
incorrect assumption as the caller is free to pick any pipe format. Use the
bpp supplied to us through util_format_get_blocksizebits().

Fixes: 3b176c44 "gallium: Add a dumb drm/kms winsys backed swrast provider"
Signed-off-by: Kevin Strasser <kevin.strasser@intel.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>
10 jobs for !977 with fix_dumb_buffer_bpp in 12 minutes and 53 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Containers Build
passed #354777
debian

00:00:22

 
  Build+Test
passed #354779
meson-clang

00:08:47

passed #354783
meson-clover

00:07:34

passed #354782
meson-main

00:04:53

passed #354778
meson-swr-glvnd

00:05:59

passed #354784
meson-vulkan

00:01:46

passed #354786
scons-llvm

00:03:58

passed #354785
scons-nollvm

00:07:21

passed #354780
scons-swr

00:05:58

passed #354781
scons-win64

00:09:53