RISC-V: Fix wrong zifencei handling in riscv_subset_list::to_string

This issue cause zifencei never correctly appended on the ISA string.

gcc/ChangeLog

	* common/config/riscv/riscv-common.c (riscv_subset_list::to_string): Fix
	wrong marco checking.

gcc/common/config/riscv/riscv-common.c

@@ -422,7 +422,7 @@ riscv_subset_list::to_string (bool version_p) const
   /* Skip since older binutils doesn't recognize zicsr.  */
   skip_zicsr = true;
 #endif
-#ifndef HAVE_AS_MARCH_ZIFENCE
+#ifndef HAVE_AS_MARCH_ZIFENCEI
   /* Skip since older binutils doesn't recognize zifencei, we made
      a mistake in that binutils 2.35 supports zicsr but not zifencei.  */
   skip_zifencei = true;