usb/hcd: remove unnecessary local_irq_save

Remove the use of local_irq_save() and IRQF_DISABLED, no longer needed since
interrupt handlers are always run with interrupts disabled on the
current CPU.

Tested successfully with 3.12.0-rc4 on my PC. Didn't find
any issue because of this change.

Signed-off-by: Michael Opdenacker <michael.opdenacker@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>