iio:trigger:interrupt fix formatting of rsize variable in name

The name includes irq_res->start which of type resource_size_t not integer.
We could in theory use %pa for this but then it would be in hex and also
that causes a warning about incorrect types anyway.  Hence just
use the irq local variable we assigned the line above.

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>