drm/panel: simple: Fix data type in KEO TX31D200VM0BAA timings

All values in a struct struct timing_entry (every entry in
struct display_timing) require an integer. Choose the closest
safe integer of 32.

This avoids a warning seen with clang:
  drivers/gpu/drm/panel/panel-simple.c:1250:27: warning: implicit
       conversion from 'double' to 'u32' (aka 'unsigned int')
       changes value from 33.5 to 33 [-Wliteral-conversion]
         .vfront_porch = { 6, 21, 33.5 },
                         ~        ^~~~
  drivers/gpu/drm/panel/panel-simple.c:1251:26: warning: implicit
        conversion from 'double' to 'u32' (aka 'unsigned int')
        changes value from 33.5 to 33 [-Wliteral-conversion]
          .vback_porch = { 6, 21, 33.5 },
                         ~        ^~~~

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180419212003.8155-1-stefan@agner.ch