drm/xe/oa: Set stream->pollin in xe_oa_buffer_check_unlocked

drm/xe/oa: Set stream->pollin in xe_oa_buffer_check_unlocked

We rely on stream->pollin to decide whether or not to block during
poll/read calls. However, currently there are blocking read code paths
which don't even set stream->pollin. The best place to consistently set
stream->pollin for all code paths is therefore to set it in
xe_oa_buffer_check_unlocked.

Fixes: e936f885f1e9 ("drm/xe/oa/uapi: Expose OA stream fd")
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Jonathan Cavitt <jonathan.cavitt@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250115222029.3002103-1-ashutosh.dixit@intel.com