entry: Fixup irqentry_enter() comment

irq_enter_from_user_mode() was changed to irqentry_enter_from_user_mode().
Update the comment within irqentry_enter() to reflect this change.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20201028163632.965518-1-ira.weiny@intel.com