drm/amdkfd: Fix boolreturn.cocci warnings

Return statements in functions returning bool should use
true/false instead of 1/0.

drivers/gpu/drm/amd/amdkfd/kfd_int_process_v9.c:40:9-10:
WARNING: return of 0/1 in function 'event_interrupt_isr_v9' with return type bool

Generated by: scripts/coccinelle/misc/boolreturn.cocci

Signed-off-by: Aishwarya Ramakrishnan <aishwaryarj100@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>