iio: adc: stm32: Fix ADCs iteration in irq handler

The irq handler was only checking the mask for the first ADCs in the case of the
F4 and H7 generation, since it was iterating up to the num_irq value. This patch add
the maximum number of ADC in the common register, which map to the number of entries of
eoc_msk and ovr_msk in stm32_adc_common_regs. This allow the handler to check all ADCs in
that module.

Tested on a STM32F429NIH6.

Fixes: 695e2f5c

 ("iio: adc: stm32-adc: fix a regression when using dma and irq")
Signed-off-by: Yannick Brosseau <yannick.brosseau@gmail.com>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Link: https://lore.kernel.org/r/20220516203939.3498673-2-yannick.brosseau@gmail.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>