x86: call32: Append appropriate suffixes

Assembler is not happy:

arch/x86/cpu/call32.S: Assembler messages:
arch/x86/cpu/call32.S:36: Warning: no instruction mnemonic suffix given and no register operands; using default for `retf'

Fix this by adding appropriate suffixes to the assembler commands.

Fixes: 6f92ed8f ("x86: Add a way to call 32-bit code from 64-bit mode")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>