CI check error: use of uninitialized value ‘string’

[bardliao]

sound/soc/sof/debug-dsp-ops.c:216:19: error: use of uninitialized value ‘string’ [CWE-457] [-Werror=analyzer-use-of-uninitialized-value]
  216 |         if (*ppos || !string)
      |             ~~~~~~^~~~~~~~~~
  ‘sof_dsp_ops_tester_dfs_read’: events 1-11
    |
    |  181 |         const char *string;
    |      |                     ^~~~~~
    |      |                     |
    |      |                     (1) region created on stack here
    |      |                     (2) capacity: 8 bytes
    |......
    |  186 |         if (!strcmp(dentry->d_name.name, "fw_filename")) {
    |      |            ~         
    |      |            |
    |      |            (3) following ‘false’ branch (when the strings are non-equal)...
    |  187 |                 string = sdev->test_profile.fw_name;
    |  188 |         } else if (!strcmp(dentry->d_name.name, "fw_path")) {
    |      |                   ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    |      |                   | |
    |      |                   | (4) ...to here
    |      |                   (5) following ‘false’ branch (when the strings are non-equal)...
    |  189 |                 string = sdev->test_profile.fw_path;
    |  190 |         } else if (!strcmp(dentry->d_name.name, "dsp_power_state")) {
    |      |                   ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    |      |                   | |
    |      |                   | (6) ...to here
    |      |                   (7) following ‘true’ branch (when the strings are equal)...
    |  191 |                 switch (sdev->dsp_power_state.state) {
    |      |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~
    |      |                                              |
    |      |                                              (8) ...to here
    |......
    |  216 |         if (*ppos || !string)
    |      |            ~~~~~~~~~~~~~~~~~
    |      |            |      |
    |      |            |      (10) ...to here
    |      |            |      (11) use of uninitialized value ‘string’ here
    |      |            (9) following ‘false’ branch...
    |

Potential fix: #5289