panfrost: Avoid double unlock.

Fix defect reported by Coverity Scan.

Double unlock (LOCK)
double_unlock: pthread_mutex_unlock unlocks dev->indirect_draw_shaders.lock while it is unlocked.

Fixes: 2e6d94c1 ("panfrost: Add helpers to support indirect draws")
Suggested-by: Alyssa Rosenzweig <alyssa@collabora.com>
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Part-of: <!14262>
47 jobs for !14262 with fix-cid-1494534 in 16 minutes and 57 seconds (queued for 19 seconds)
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