Revert "uio: use request_threaded_irq instead"

Since mutex lock in irq hanler is useless currently, here will
remove it together with it.

This reverts commit 9421e45f

.

Reported-by:  <james.r.harris@intel.com>
CC: Ahsan Atta <ahsan.atta@intel.com>
Signed-off-by: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>