PM / Hibernate: Swap, remove useless check from swsusp_read()

It will never reach here if the sws_resume_bdev is erratic.
swsusp_read() is called only from software_resume(), but after
swsusp_check() which would catch the error state.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>