amdgcn: Fix 64-bit vector multiply Fix an old maths bug with DImode vector multiply. Backport from mainline. gcc/ChangeLog: * config/gcn/gcn-valu.md (mul<mode>3): Remove erroneous hi*hi step. (mul<mode>3_dup): Likewise. (mul<mode>3_exec): Likewise. (mul<mode>3_dup_exec): Likewise. (cherry picked from commit 0a1f6acb90e27ac0b2984ad6841186ca54bc5725)