Preserve SECONDS fields when clearing Clock Halt bit at initialisation (#77354)

[clodnut]

drivers: rtc: rtc_1307.c

Read/modify/write the CH/SECONDS register at initialisation to clear only the Clock Halt bit and only if it is set.

This prevents the SECONDS field(s) from being wiped out unconditionally at initialisation.

Fixes #77354.

[github-actions]

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[bjarki-andreasen]

Hi, you need to squash your commits and force push the single commit, and make the header of said commit a bit more descriptive :)