drm/komeda: Use IRQ_RETVAL shorthand in d71_irq_handler

No change in behaviour; IRQ_RETVAL is about twice as popular as
manually writing out the ternary.

Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
Reviewed-by: James Qian Wang (Arm Technology China) <james.qian.wang@arm.com>
Signed-off-by: Ayan kumar halder <ayan.halder@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190920151247.25128-1-mihail.atanassov@arm.com