target/riscv/csr.c: fix OVERFLOW_BEFORE_WIDEN in rmw_sctrdepth()

Coverity found the following issue:

  >>>     CID 1593156:  Integer handling issues  (OVERFLOW_BEFORE_WIDEN)
  >>>     Potentially overflowing expression "0x10 << depth" with type
  "int" (32 bits, signed) is evaluated using 32-bit arithmetic, and then
  used in a context that expects an expression of type "uint64_t" (64
  bits, unsigned).
  4299             depth = 16 << depth;

Fix it by forcing the expression to be 64 bits wide by using '16ULL'.

Resolves: Coverity CID 1593156
Fixes: c48bd18eae ("target/riscv: Add support for Control Transfer Records extension CSRs.")
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250307124602.1905754-1-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/csr.c

@@ -4302,7 +4302,7 @@ static RISCVException rmw_sctrdepth(CPURISCVState *env, int csrno,
         }
 
         /* Update sctrstatus.WRPTR with a legal value */
-        depth = 16 << depth;
+        depth = 16ULL << depth;
         env->sctrstatus =
             env->sctrstatus & (~SCTRSTATUS_WRPTR_MASK | (depth - 1));
     }