[frameworks][av] fix -Wimplicit-int-float-conversion

IEEE754 single precision cannot precisely represent
INT32_MAX/UINT_MAX/RAND_MAX.

IEEE754 double precision cannot precisely represent INT64_MAX.

As such, implicit conversions from operations with floating point and
integral operands may result in a loss of precision.

Accept the imprecision with by making the existing implicit casts
explicit.

Bug: 139945549
Test: mm
Change-Id: Ic66b3d3bbac9e644e27ad8233018f24dfce3209f
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>