regmap-irq: Use the new num_config_regs property in regmap_add_irq_chip_fwnode

In the Linux kernel, the following vulnerability has been resolved:

regmap-irq: Use the new num_config_regs property in regmap_add_irq_chip_fwnode

Commit faa87ce9196d ("regmap-irq: Introduce config registers for irq
types") added the num_config_regs, then commit 9edd4f5aee84 ("regmap-irq:
Deprecate type registers and virtual registers") suggested to replace
num_type_reg with it. However, regmap_add_irq_chip_fwnode wasn't modified
to use the new property. Later on, commit 255a03bb1bb3 ("ASoC: wcd9335:
Convert irq chip to config regs") removed the old num_type_reg property
from the WCD9335 driver's struct regmap_irq_chip, causing a null pointer
dereference in regmap_irq_set_type when it tried to index d->type_buf as
it was never allocated in regmap_add_irq_chip_fwnode:

[ 39.199374] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000

[ 39.200006] Call trace:
[ 39.200014] regmap_irq_set_type+0x84/0x1c0
[ 39.200026] __irq_set_trigger+0x60/0x1c0
[ 39.200040] __setup_irq+0x2f4/0x78c
[ 39.200051] request_threaded_irq+0xe8/0x1a0

Use num_config_regs in regmap_add_irq_chip_fwnode instead of num_type_reg,
and fall back to it if num_config_regs isn't defined to maintain backward
compatibility.