staging: sm750fb: constify fix_id array

staging: sm750fb: constify fix_id array

Add the missing 'const' qualifier to the static fix_id array to ensure
the pointer array itself is immutable.

Originally:
    static const char *fix_id[2];
The strings are constant, but the pointer array itself is writable.

With the change:
    static const char * const fix_id[2];
Both the strings and the pointer array are immutable, allowing the
compiler to treat the object as read-only.

Verified by inspecting the generated object file with 'nm':

    00000000000002b8 0000000000000010 r fix_id.3

The 'r' flag indicates the symbol is placed in a read-only section.

This does not change runtime behavior as fix_id is never modified.

Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
Link: https://patch.msgid.link/20260401115024.89-1-dennylin0707@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>