Directly converting from a float to an 8 bit integer and from a 64 bit
float to an integer smaller than 32 bit is not supported, therefore add
an intermediate conversion to an 32 bit integer.
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18109>