[media] v4l2-dev.rst: adjust table to fit into page

One table here is not being properly displayed on LaTeX
format. Adjust it.
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/media/kapi/v4l2-dev.rst

@@ -262,6 +262,7 @@ file operations.
 
 It is a bitmask and the following bits can be set:
 
+.. tabularcolumns:: |p{5ex}|L|
 
 ===== ================================================================
 Mask  Description