Fix tdpbf16ps testcase

gcc/testsuite/ChangeLog:

	* gcc.target/i386/amx-check.h (check_float_tile_register):
	New check function for float to prevent precision loss.
	* gcc.target/i386/amxbf16-dpbf16ps-2.c: Correct the type convert
	and byte offset. Use the new check function.