USB: yurex: add .llseek fop to file_operations

Default llseek operation behavior was changed by the patch named
"vfs: make no_llseek the default" after the yurex driver had been merged,
so the llseek to yurex is now ignored.

This patch add llseek fop with default_llseek to yurex driver
to catch up to the change.

Signed-off-by: Tomoki Sekiyama <tomoki.sekiyama@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>