[archiso] mkarchiso: Use truncate instead of dd

Signed-off-by: Gerardo Exequiel Pozzi <vmlinuz386@yahoo.com.ar>

archiso/mkarchiso

@@ -326,7 +326,7 @@ _mkfs () {
 
     _msg_info "Creating ${_fs_type} image of ${_fs_size} MiB..."
     rm -f "${_fs_img}"
-    dd of="${_fs_img}" count=0 bs=1M seek=${_fs_size} &> /dev/null
+    truncate -s ${_fs_size}M "${_fs_img}"
     local _qflag=""
     if [[ ${quiet} == "y" ]]; then
         _qflag="-q"