firmware: arm_sdei: Cleanup on cross call function

This applies cleanup on the cross call functions, no functional
changes are introduced:

   * Wrap the code block of CROSSCALL_INIT inside "do { } while (0)"
     as linux kernel usually does. Otherwise, scripts/checkpatch.pl
     reports warning regarding this.
   * Use smp_call_func_t for @fn argument in sdei_do_cross_call()
     as the function is called on target CPU(s).
   * Remove unnecessary space before @event in sdei_do_cross_call()

Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: James Morse <james.morse@arm.com>
Link: https://lore.kernel.org/r/20200922130423.10173-11-gshan@redhat.com


Signed-off-by: Will Deacon <will@kernel.org>