drm/amdkfd: Return true/false (not 1/0) from bool functions

Return boolean values ("true" or "false") instead of 1 or 0 from bool
functions. This fixes the following warnings from coccicheck:

./drivers/gpu/drm/amd/amdkfd/kfd_int_process_v11.c:244:9-10: WARNING:
return of 0/1 in function 'event_interrupt_isr_v11' with return type
bool

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>