ep93xx: clock: Do not return the address of the freed memory

Avoid return freed memory addresses,Modified to the actual error
return value of clk_register().

Fixes: 9645ccc7 ("ep93xx: clock: convert in-place to COMMON_CLK")
Signed-off-by: Genjian Zhang <zhanggenjian@kylinos.cn>
Acked-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>