perf: arm-ni: Fix an NULL vs IS_ERR() bug

The devm_ioremap() function never returns error pointers, it returns a
NULL pointer if there is an error.

Fixes: 4d5a7680 ("perf: Add driver for Arm NI-700 interconnect PMU")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/04d6ccc3-6d31-4f0f-ab0f-7a88342cc09a@stanley.mountain


Signed-off-by: Will Deacon <will@kernel.org>