Fix indentation in dd(1)

Quoting http://mdocml.bsd.lv/mdoc/details/width.html

Do not use macros in the argument specifying the width,
since that's not portable.  While GNU troff can handle it,
mandoc cannot.

MFC after:	3 days
Sponsored by:	Dell EMC

bin/dd/dd.1

@@ -32,7 +32,7 @@
 .\"     @(#)dd.1	8.2 (Berkeley) 1/13/94
 .\" $FreeBSD$
 .\"
-.Dd October 5, 2016
+.Dd April 2, 2017
 .Dt DD 1
 .Os
 .Sh NAME
@@ -54,7 +54,7 @@ displays the number of complete and partial input and output blocks
 and truncated input records to the standard error output.
 .Pp
 The following operands are available:
-.Bl -tag -width ".Cm of Ns = Ns Ar file"
+.Bl -tag -width "of=file"
 .It Cm bs Ns = Ns Ar n
 Set both input and output block size to
 .Ar n
@@ -164,7 +164,7 @@ bytes per second.
 Where
 .Cm value
 is one of the symbols from the following list.
-.Bl -tag -width ".Cm noxfer"
+.Bl -tag -width "noxfer"
 .It Cm noxfer
 Do not print the transfer statistics as the last line of status output.
 .It Cm none
@@ -175,7 +175,7 @@ Error messages are shown; informational messages are not.
 Where
 .Cm value
 is one of the symbols from the following list.
-.Bl -tag -width ".Cm unblock"
+.Bl -tag -width "unblock"
 .It Cm ascii , oldascii
 The same as the
 .Cm unblock
@@ -459,4 +459,4 @@ subsystem might prevent the super-user from writing blocks to a disk.
 Instructions for temporarily disabling these protection mechanisms can be
 found in the
 .Xr geom 4
-manpage.
+man page.