tests/tcg/i386: Use explicit suffix on fist insns

Fixes a number of assembler warnings of the form:

test-i386.c: Assembler messages:
test-i386.c:869: Warning: no instruction mnemonic suffix given
  and no register operands; using default for `fist'

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220527171143.168276-1-richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220613171258.1905715-3-alex.bennee@linaro.org>