drm/vmwgfx: use min_t to replace min

Use min_t to replace min, min_t is a bit fast because min use
twice typeof.
This patch also fix check_patch.pl warning:
WARNING: min() should probably be min_t(unsigned long, num_pages,
VMW_PPN_PER_REMAP)
+unsigned long nr = min(num_pages, (unsigned long)
VMW_PPN_PER_REMAP);

Signed-off-by: Bernard Zhao <bernard@vivo.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201119011146.107587-1-bernard@vivo.com