drm/vmwgfx: Handle surface check failure correctly

Currently if condition (!bo and !vmw_kms_srf_ok()) was met
we go to err_out with ret == 0.
err_out dereferences vfb if ret == 0, but in our case vfb is still NULL.

Fix this by assigning sensible error to ret.

Found by Linux Verification Center (linuxtesting.org) with SVACE

Signed-off-by: Nikolay Kuratov <kniv@yandex-team.ru>
Cc: stable@vger.kernel.org
Fixes: 810b3e16 ("drm/vmwgfx: Support topology greater than texture size")
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241002122429.1981822-1-kniv@yandex-team.ru