drm/vmwgfx: Pass along the format info from .fb_create() to drm_helper_mode_fill_fb_struct()

Plumb the format info from .fb_create() all the way to
drm_helper_mode_fill_fb_struct() to avoid the redundant
lookup.

Cc: Zack Rusin <zack.rusin@broadcom.com>
Cc: Broadcom internal kernel review list <bcm-kernel-feedback-list@broadcom.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250701090722.13645-19-ville.syrjala@linux.intel.com