drivers: net: qti-can: Use div_u64 for 64-bit division

Use div_u64 to avoid compilation error in 32-bit
architectures.

Change-Id: I2a247dff5ee0a601deaee9e3375c5026788ef2df
Signed-off-by: Aditya Mathur <aditmath@codeaurora.org>
Signed-off-by: Gustavo Solaira <gustavos@codeaurora.org>