doc-rst: subdev-formats: Improve figure caption

Add a numbering for the figure.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/linux_tv/media/v4l/subdev-formats.rst

@@ -2760,9 +2760,7 @@ be named ``MEDIA_BUS_FMT_SRGGB10_2X8_PADHI_LE``.
     :alt:    bayer.png
     :align:  center
 
-    Bayer Patterns
-
-    Bayer filter color patterns
+    **Figure 4.8 Bayer Patterns**