ieee802154: Fix build error

ieee802154: Fix build error

If REGMAP_SPI is m and IEEE802154_MCR20A is y,

	mcr20a.c:(.text+0x3ed6c5b): undefined reference to `__devm_regmap_init_spi'
	ld: mcr20a.c:(.text+0x3ed6cb5): undefined reference to `__devm_regmap_init_spi'

Select REGMAP_SPI for IEEE802154_MCR20A to fix it.

Fixes: 8c6ad9cc5157 ("ieee802154: Add NXP MCR20A IEEE 802.15.4 transceiver driver")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Link: https://lore.kernel.org/20240909131740.1296608-1-ruanjinjie@huawei.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>