markup_oops.pl: minor fixes

1. Fix a little format issue.
2. Check the return of "Getopt::Long::GetOptions".  Output usage and
   exit if it get error.
3. Change $ARGV[$#ARGV] to $ARGV[0].
4. Change the code which get $modulefile from modinfo.  Replace the
   pipeline with `modinfo -F filename $module`.
4. Change usage from "Specify the module directory name" to "Specify the
   module filename".

Signed-off-by: Hui Zhu <teawater@gmail.com>
Signed-off-by: Michal Marek <mmarek@suse.cz>