drivers:char:ipmi: Remove unneeded FIXME comment in the file,ipmi_si_intf.c

Removes a no longer needed FIXME comment in the function,acpi_gpe_irq_setup
for the file,ipmi_si_intf.c. This comment is no longer needed as clearly we
are passing the correct level of  ACPI_GPE_LEVEL_TRIGGERED to the installer
function,acpi_install_gpe_handler due to no breakage after years of using
this ACPI level in the function,acpi_install_gpe_handler.

Signed-off-by: Nicholas Krause <xerofoify@gmail.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>