[RISCV] Remove a use of getMinVLen in favor of getRealMinVLen

The later is possibly greater than the former, and thus the assert was overly strong when a wider VLEN was set at the command line.

llvm/lib/Target/RISCV/RISCVISelLowering.cpp

@@ -3185,7 +3185,7 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
     // minimum size. e.g. <vscale x 2 x i32>. VLENB is in bytes so we calculate
     // vscale as VLENB / 8.
     static_assert(RISCV::RVVBitsPerBlock == 64, "Unexpected bits per block!");
-    if (Subtarget.getMinVLen() < RISCV::RVVBitsPerBlock)
+    if (Subtarget.getRealMinVLen() < RISCV::RVVBitsPerBlock)
       report_fatal_error("Support for VLEN==32 is incomplete.");
     // We assume VLENB is a multiple of 8. We manually choose the best shift
     // here because SimplifyDemandedBits isn't always able to simplify it.