[media] DocBook: fix some syntax issues at dvbproperty.xml

Some minor English syntax fixes.
Reported-by: NJonathan Corbet <corbet@lwn.net>
Signed-off-by: NMauro Carvalho Chehab <mchehab@osg.samsung.com>

Documentation/DocBook/media/dvb/dvbproperty.xml

 <section id="frontend-properties">
 <title>DVB Frontend properties</title>
 <para>Tuning into a Digital TV physical channel and starting decoding it
-    requires to change a set of parameters, in order to control the
+    requires changing a set of parameters, in order to control the
     tuner, the demodulator, the Linear Low-noise Amplifier (LNA) and to set the
     antenna subsystem via Satellite Equipment Control (SEC), on satellite
     systems. The actual parameters are specific to each particular digital
-    TV standards, and may change as the digital TV specs evolutes.</para>
-<para>In the past, the strategy used were to have an union with the parameters
+    TV standards, and may change as the digital TV specs evolves.</para>
+<para>In the past, the strategy used was to have a union with the parameters
     needed to tune for DVB-S, DVB-C, DVB-T and ATSC delivery systems grouped
     there. The problem is that, as the second generation standards appeared,
     those structs were not big enough to contain the additional parameters.