Fix typo in bsdcpio manual:

s/libarchive_formats/libarchive-formats

PR:		150300
Submitted by:	Kurt Jaeger <fbsd-pr at opsec dot eu>
Patch by:	Kurt Jaeger
Approved by:	keramida (mentor)
MFC after:	1 week

usr.bin/cpio/bsdcpio.1

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd December 21, 2007
+.Dd September 5, 2010
 .Dt BSDCPIO 1
 .Os
 .Sh NAME
@@ -140,7 +140,7 @@ The POSIX.1 tar format.
 The default format is
 .Ar odc .
 See
-.Xr libarchive_formats 5
+.Xr libarchive-formats 5
 for more complete information about the
 formats currently supported by the underlying
 .Xr libarchive 3