PM / hibernate: Documentation: Fix script for unswapping

System can have mmaped also character devices (e.g dri devices by X) or deleted
files. Running cat on character devices is really bad idea (system can hang) so
run cat only on regular files. Also mmaped files can have spaces in filenames.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
[rjw: Subject]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Documentation/power/swsusp.txt

@@ -220,7 +220,10 @@ Q: After resuming, system is paging heavily, leading to very bad interactivity.
 
 A: Try running
 
-cat `cat /proc/[0-9]*/maps | grep / | sed 's:.* /:/:' | sort -u` > /dev/null
+cat /proc/[0-9]*/maps | grep / | sed 's:.* /:/:' | sort -u | while read file
+do
+  test -f "$file" && cat "$file" > /dev/null
+done
 
 after resume. swapoff -a; swapon -a may also be useful.