fix: div_buf_cur assigned twice when rtl_sdr_blog feature is enabled

[abc8747]

Fixes compile issue:

$ cargo check --features rtl_sdr_blog
error[E0384]: cannot assign twice to immutable variable `div_buf_cur`
   --> src/tuners/r82xx.rs:906:13
    |
886 |                 div_buf_cur = 0x30; /* 11, 150u */
    |                 ------------------ first assignment to `div_buf_cur`
...
906 |             div_buf_cur = 0xa0;
    |             ^^^^^^^^^^^^^^^^^^ cannot assign twice to immutable variable
    |

[ccostes]

Thanks for the fix!