doc-rst: media-controller-model: fix a typo

Remove a 'm' at the end of the last phrase.
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/linux_tv/media/mediactl/media-controller-model.rst

@@ -32,4 +32,4 @@ are:
    from a source pad to a sink pad.
 
 -  An **interface link** is a point-to-point bidirectional control
-   connection between a Linux Kernel interface and an entity.m
+   connection between a Linux Kernel interface and an entity.