Correctly format page cross references

Most pages in util-linux follow the standard convention
of formatting page cross references in bold. Fix the
few exceptions that use italic.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

login-utils/chfn.1

@@ -72,7 +72,7 @@ Display version information and exit.
 .SH CONFIG FILE ITEMS
 .B chfn
 reads the
-.IR /etc\:/login.defs (5)
+.BR /etc\:/login.defs (5)
 configuration file.  Note that the configuration file could be
 distributed with another package (e.g. shadow-utils).  The following
 configuration items are relevant for

login-utils/login.1

@@ -136,7 +136,7 @@ Display version information and exit.
 .SH CONFIG FILE ITEMS
 .B login
 reads the
-.IR /etc\:/login.defs (5)
+.BR /etc\:/login.defs (5)
 configuration file.  Note that the configuration file could be
 distributed with another package (e.g. shadow-utils).  The following
 configuration items are relevant for

sys-utils/mount.8

@@ -780,7 +780,7 @@ and
 For most types all the
 .B mount
 program has to do is issue a simple
-.IR mount (2)
+.BR mount (2)
 system call, and no detailed knowledge of the filesystem type is required.
 For a few types however (like nfs, nfs4, cifs, smbfs, ncpfs) an ad hoc code is
 necessary.  The nfs, nfs4, cifs, smbfs, and ncpfs filesystems

text-utils/pg.1

@@ -25,7 +25,7 @@ reads from standard input.
 If standard output is not a terminal,
 .B pg
 acts like
-.IR cat (1)
+.BR cat (1)
 but precedes each file with its name if there is more than one.
 .PP
 If input comes from a pipe,
@@ -206,7 +206,7 @@ Overrides the system-supplied number of columns if set.
 .TP
 .BR LANG ,\  LC_ALL ,\  LC_COLLATE ,\  LC_CTYPE ,\  LC_MESSAGES
 See
-.IR locale (7).
+.BR locale (7).
 .TP
 .B LINES
 Overrides the system-supplied number of lines if set.