tty: serial: samsung_tty: Fix a memory leak in s3c24xx_serial_getclk() when iterating clk

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

tty: serial: samsung_tty: Fix a memory leak in s3c24xx_serial_getclk() when iterating clk

When the best clk is searched, we iterate over all possible clk.

If we find a better match, the previous one, if any, needs to be freed. If a better match has already been found, we still need to free the new one, otherwise it leaks.