USB: ehci: omap: use default interrupt threshold

The current driver reduces the interrupt threshold to 1 microframe.
This was an accidental change and is not really required.
The default of 8 microframes will do just fine. So change it back.

Signed-off-by: Anand Gadiyar <gadiyar@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>