intel/compiler: Actually retype integer sources of sampler message payload

According to PRMs: "All parameters are of type IEEE_Float, except those in the The ld*, resinfo, and the offu, offv of the gather4_po[_c] instruction message types, which are of type signed integer."

Currently, we load parameters with the correct types, but use them as send sources with the default float type, which may confuse passes downstream. Fix this by actually storing the retyped sources.

Closes: #11118 (closed)

Cc @llandwerlin