busybox: Fix cut with "-s" flag

This fixes and issue that allows blank lines to be incorrectly output
when the "-s" flag is included. This issue propogates into the
populate-volatile.sh script in initscripts. If a volatiles drop file
contains blank lines, a blank line will be included in combined users,
which will incorrectly result in a difference in the number of combined
users versus defined users. If this happens, the volatiles file will not
be executed.

Signed-off-by: Colin McAllister <colinmca242@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>