drm/xe/vsec: Address static checker issue

The callback structure should be static.

Add static attribute.

Fixes: 0c45e76fcc62 ("drm/xe/vsec: Support BMG devices")
Reported-by: kernel test robot <[e-mail]>
Closes: https://lore.kernel.org/oe-kbuild-all/[e-mail]/
Signed-off-by: Michael J. Ruhl <[e-mail]>
Reviewed-by: Rodrigo Vivi <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Signed-off-by: Rodrigo Vivi <[e-mail]>

drivers/gpu/drm/xe/xe_vsec.c

···
 	return count;
 }
 
-struct pmt_callbacks xe_pmt_cb = {
+static struct pmt_callbacks xe_pmt_cb = {
 	.read_telem = xe_pmt_telem_read,
 };