irqchip/ls-extirq: Fix devm_of_iomap() error check

irqchip/ls-extirq: Fix devm_of_iomap() error check

The devm_of_iomap() function returns an ERR_PTR() encoded error code on
failure. Replace the incorrect check against NULL with IS_ERR().

Fixes: 05cd654829dd ("irqchip/ls-extirq: Convert to a platform driver to make it work again")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Herve Codina <herve.codina@bootlin.com>
Link: https://patch.msgid.link/20260224113610.1129022-3-ioana.ciornei@nxp.com
Closes: https://lore.kernel.org/all/aYXvfbfT6w0TMsXS@stanley.mountain/