target/riscv/csr.c: fix deadcode in aia_smode32()

Coverity reported a DEADCODE ticket in this function, as follows:

 >>>>      CID 1590358:  Control flow issues  (DEADCODE)
 >>>>      Execution cannot reach this statement: "return ret;".
 > 380             return ret;
 > 381         }

The cause is that the 'if (ret != RISCV_EXCP_NONE)' conditional is
duplicated:

    ret = smstateen_acc_ok(env, 0, SMSTATEEN0_AIA);
    if (ret != RISCV_EXCP_NONE) {
        return ret;
    }

    if (ret != RISCV_EXCP_NONE) {
        return ret;
    }

Remove the duplication to fix the deadcode.

Resolves: Coverity CID 1590358
Fixes: dbcb6e1ccf ("target/riscv: Enable S*stateen bits for AIA")
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20250121184847.2109128-5-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

target/riscv/csr.c

@@ -376,10 +376,6 @@ static RISCVException aia_smode32(CPURISCVState *env, int csrno)
         return ret;
     }
 
-    if (ret != RISCV_EXCP_NONE) {
-        return ret;
-    }
-
     return smode32(env, csrno);
 }