MLK-20201 clk: imx: Fix coverity issue of CID 17326/17327

MLK-20201 clk: imx: Fix coverity issue of CID 17326/17327

This patch fixes below coverity issues:

CID 17326/17327: Unintentional integer overflow (OVERFLOW_BEFORE_WIDEN)
overflow_before_widen: Potentially overflowing expression div *
parent_rate with type unsigned long (32 bits, unsigned) is evaluated
using 32-bit arithmetic, and then used in a context that expects an
expression of type u64 (64 bits, unsigned).

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Reviewed-by: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Arulpandiyan Vadivel <arulpandiyan_vadivel@mentor.com>
Signed-off-by: Shrikant Bobade <Shrikant_Bobade@mentor.com>
(cherry picked from commit 4bb630c8543c9346a0c21b4e42ad3949e7c6185d)