[openEuler-1.0-LTS] 修复swiotlb导致panic的问题

After patch ddbd89deb7d3 ("swiotlb: fix info leak with DMA_FROM_DEVICE"),           
swiotlb_bounce will be called in swiotlb_tbl_map_single unconditionally.            
This requires that the physical address must be valid, which is not always          
true on stable-4.19 or earlier version.                                             
On stable-4.19, swiotlb_alloc_buffer will call swiotlb_tbl_map_single with          
orig_addr equal to zero, which cause such a panic:                                  
                                                                                    
Unable to handle kernel paging request at virtual address ffffb77a40000000          
...                                                                                 
pc : __memcpy+0x100/0x180                                                           
lr : swiotlb_bounce+0x74/0x88                                                       
...                                                                                 
Call trace:                                                                         
 __memcpy+0x100/0x180                                                               
 swiotlb_tbl_map_single+0x2c8/0x338                                                 
 swiotlb_alloc+0xb4/0x198                                                           
 __dma_alloc+0x84/0x1d8                                                             
 ...                                                                                
                                                                                    
On stable-4.9 and stable-4.14, swiotlb_alloc_coherent wille call map_single         
with orig_addr equal to zero, which can cause same panic.                           
                                                                                    
Fix this by skipping swiotlb_bounce when orig_addr is zero.

GVP openEuler/kernel

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GVPopenEuler/kernel

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