[nrfconnect] Fix setting pincode based on kconfig.

[kkasperczyk-no]

Currently the CONFIG_CHIP_DEVICE_PAIRING_PASSCODE is used for setting pincode, but such symbol doesn't exist anymore. Used correct CONFIG_CHIP_DEVICE_SPAKE2_PASSCODE symbol instead.

[github-actions]

PR #23172: Size comparison from 2c9cd92 to 3d26596

Increases (2 builds for qpg, telink)

platform	target	config	section	2c9cd92	3d26596	change	% change
qpg	lighting-app	qpg6105+debug	(read/write)	1148624	1148632	8	0.0
			.text	595724	595732	8	0.0
telink	ota-requestor-app	tlsr9518adk80d	text	577540	577542	2	0.0

Full report (5 builds for qpg, telink)

platform	target	config	section	2c9cd92	3d26596	change	% change
qpg	lighting-app	qpg6105+debug	(read/write)	1148624	1148632	8	0.0
			.bss	110556	110556	0	0.0
			.data	832	832	0	0.0
			.text	595724	595732	8	0.0
	lock-app	qpg6105+debug	(read/write)	1113712	1113712	0	0.0
			.bss	106372	106372	0	0.0
			.data	836	836	0	0.0
			.text	560808	560808	0	0.0
telink	light-switch-app	tlsr9518adk80d	(read/write)	789364	789364	0	0.0
			bss	72480	72480	0	0.0
			noinit	43520	43520	0	0.0
			text	553136	553136	0	0.0
	lighting-app	tlsr9518adk80d	(read/write)	811468	811468	0	0.0
			bss	73328	73328	0	0.0
			noinit	43520	43520	0	0.0
			text	571354	571354	0	0.0
	ota-requestor-app	tlsr9518adk80d	(read/write)	819412	819412	0	0.0
			bss	74236	74236	0	0.0
			noinit	43520	43520	0	0.0
			text	577540	577542	2	0.0