If the driver is used on an ARM platform with SPARSE_IRQ defined,
semantics of NR_IRQS is different (minimal value of virtual irqs)
and by default it is set to 16, see arch/arm/include/asm/irq.h.

This value may be less than the actual number of virtual irqs, which
may break the driver initialization. The check removal allows to use
the driver on such a platform, and, if irq controller driver works
correctly, the check is not needed on legacy platforms.

Fixes a runtime problem:

  rtc-lpc32xx 40024000.rtc: Can't get interrupt resource

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>