devm_ioremap_resource() never returns NULL pointer, it
will return ERR_PTR() when it fails, so replace the check
with IS_ERR().

Fixes: 5b791662 ("Coresight: Add TPDA link driver")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
[ Fix return value to the PTR_ERR(base) ]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230129084246.537694-1-yangyingliang@huawei.com