drm/etnaviv: Drop the 'struct etnaviv_iommu_global::pta_lock' data member

Because it is not get used, drop it.

Signed-off-by: Sui Jingfeng <[e-mail]>
Signed-off-by: Lucas Stach <[e-mail]>

drivers/gpu/drm/etnaviv/etnaviv_mmu.h

···
 			/* P(age) T(able) A(rray) */
 			u64 *pta_cpu;
 			dma_addr_t pta_dma;
-			struct spinlock pta_lock;
 			DECLARE_BITMAP(pta_alloc, ETNAVIV_PTA_ENTRIES);
 		} v2;
 	};