drivers: Remove undesirable irq_enable calls from nrfx driver shims

Shims for nrfx drivers should only connect the related IRQ handlers,
they should not enable the IRQs, as this could lead to a situation
where the interrupt handler is called before the driver had a chance
to properly initialize the peripheral and install the provided event
handler. nrfx drivers will enable the interrupts appropriately on
their own by calling the NRFX_IRQ_ENABLE macro which is implemented
in nrfx_glue.h as a call to irq_enable().
This commit fixes the above issue spotted in the following shims:
- dmic_nrfx_pdm
- clock_control_nrf
- i2s_nrfx

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>