[GCC4] fix build error in drivers/scsi/atp870u.c

[GCC4] fix build error in drivers/scsi/atp870u.c

This patch fixes these errors with gcc 4 :

atp870u.c: In function 'send_s870':
atp870u.c:810: error: invalid lvalue in assignment
atp870u.c:811: error: invalid lvalue in assignment
atp870u.c:812: error: invalid lvalue in assignment
atp870u.c:817: error: invalid lvalue in assignment
atp870u.c:818: error: invalid lvalue in assignment
atp870u.c:819: error: invalid lvalue in assignment
atp870u.c:822: error: invalid lvalue in assignment
atp870u.c:831: error: invalid lvalue in assignment
atp870u.c:832: error: invalid lvalue in assignment
atp870u.c:833: error: invalid lvalue in assignment
atp870u.c:838: error: invalid lvalue in assignment
atp870u.c:839: error: invalid lvalue in assignment
atp870u.c:840: error: invalid lvalue in assignment