[RISCV] Fix test using wrong variable. NFC

Looks like this test was trying to check if two shifts were combined, but it
was accidentally using the insertelement instead of the splat.

Author: lukel97

llvm/test/CodeGen/RISCV/rvv/combine-splats.ll

@@ -59,20 +59,15 @@ define <vscale x 2 x i64> @or_and_nxv2i64_fold(<vscale x 2 x i64> %a0) {
 define <vscale x 4 x i32> @combine_vec_shl_shl(<vscale x 4 x i32> %x) {
 ; CHECK-LABEL: combine_vec_shl_shl:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    li a0, 2
-; CHECK-NEXT:    vsetvli a1, zero, e32, m2, ta, ma
-; CHECK-NEXT:    vmv.s.x v10, a0
-; CHECK-NEXT:    li a0, 4
-; CHECK-NEXT:    vmv.s.x v12, a0
-; CHECK-NEXT:    vsll.vv v8, v8, v10
-; CHECK-NEXT:    vsll.vv v8, v8, v12
+; CHECK-NEXT:    vsetvli a0, zero, e32, m2, ta, ma
+; CHECK-NEXT:    vsll.vi v8, v8, 6
 ; CHECK-NEXT:    ret
   %ins1 = insertelement <vscale x 4 x i32> poison, i32 2, i32 0
   %splat1 = shufflevector <vscale x 4 x i32> %ins1, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
   %ins2 = insertelement <vscale x 4 x i32> poison, i32 4, i32 0
   %splat2 = shufflevector <vscale x 4 x i32> %ins2, <vscale x 4 x i32> poison, <vscale x 4 x i32> zeroinitializer
-  %v1 = shl <vscale x 4 x i32> %x, %ins1
-  %v2 = shl <vscale x 4 x i32> %v1, %ins2
+  %v1 = shl <vscale x 4 x i32> %x, %splat1
+  %v2 = shl <vscale x 4 x i32> %v1, %splat2
   ret <vscale x 4 x i32> %v2
 }