MLK-21252 drm/bridge: sec-dsim: resolve OVERFLOW_BEFORE_WIDEN warns

Coverity reports the 'OVERFLOW_BEFORE_WIDEN' warns which can
cause potential expression overflow for multiplying two 32bit
integers and assign the result to a 64bit integer, since no
automatic integer type promotion exists before the multiply
operation, so requires explicit type casting for either one
of operands.

Signed-off-by: Fancy Fang <chen.fang@nxp.com>