From the definition of the CJNE instruction in Intel's 8051 User Manual:
"The carry flag is set if the unsigned integer value of <dest-byte> is less than the unsigned integer value of <src-byte>; otherwise,the carry is cleared."

This means that the status of the carry flag is always defined after execution of the CJNE instruction and there is no need to clear it beforehand.

Best regards,
Rob.