mtd: nand: lpc32xx: fix invalid error handling of a requested irq

Semantics of NR_IRQS is different on machines with SPARSE_IRQ option
disabled or enabled, in the latter case IRQs are allocated starting
at least from the value specified by NR_IRQS and going upwards, so
the check of (irq >= NR_IRQ) to decide about an error code returned by
platform_get_irq() is completely invalid, don't attempt to overrule
irq subsystem in the driver.

The change fixes LPC32xx NAND MLC driver initialization on boot.

Fixes: 8cb17b5e ("irqchip: Add LPC32xx interrupt controller driver")
Cc: stable@kernel.org # v4.7+
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Acked-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>