doc-rst: pixfmt-yuv422m: remove an empty column

The conversion added an empty column (probably, it was used on
DocBook just to increase spacing.

Remove it.
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/linux_tv/media/v4l/pixfmt-yuv422m.rst

@@ -188,7 +188,6 @@ Each cell is one byte.
        -  
        -  1
 
-       -  
        -  2
 
        -  
@@ -204,7 +203,6 @@ Each cell is one byte.
 
        -  Y
 
-       -  
        -  Y
 
        -  C
@@ -221,7 +219,6 @@ Each cell is one byte.
 
        -  Y
 
-       -  
        -  Y
 
        -  C
@@ -238,7 +235,6 @@ Each cell is one byte.
 
        -  Y
 
-       -  
        -  Y
 
        -  C
@@ -255,7 +251,6 @@ Each cell is one byte.
 
        -  Y
 
-       -  
        -  Y
 
        -  C