staging: hp100: Add space around operator

Add space around "-" operator to improve code readability and adhere to
the Linux kernel coding style.
Reported by checkpatch.pl

Signed-off-by: Soumyajit Deb <debsoumyajit100@gmail.com>
Link: https://lore.kernel.org/r/20200325144353.42655-1-debsoumyajit100@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>