Staging: emxx_udc: Add space around '-'

Add space around operator '-'. Problem found using checkpatch.pl
CHECK: spaces preferred around that '-' (ctx:VxV)

Signed-off-by: Dilek Uzulmez <dilekuzulmez@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>