drm/format-helper: fix build

Build fails with:

error: multiple unsequenced modifications to 'sbuf32'
[-Werror,-Wunsequenced]
  264 |                         le32_to_cpup(sbuf32++),
      |                                            ^
  265 |                         le32_to_cpup(sbuf32++),
      |                                            ~~

With that move the increment of the sbuf32 pointer to the end of the
loop, instead of inside the array list initializer, where the
order/sequence of the sbuf32 pointer modifications is not defined.

Fixes: 58523a25 ("drm/format-helper: Optimize 32-to-24-bpp conversion")
Fixes: 3f31a017 ("drm/format-helper: Optimize 32-to-16-bpp conversion")
Fixes: 65931bbc ("drm/format-helper: Optimize 32-to-8-bpp conversion")
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20250402104430.142398-2-matthew.auld@intel.com