drm/panic: remove spurious empty line

Clippy in the upcoming Rust 1.83.0 spots a spurious empty line since the
`clippy::empty_line_after_doc_comments` warning is now enabled by default
given it is part of suspicious` [1]:

    error: empty line after doc comment
       --> drivers/gpu/drm/drm_panic_qr.rs:931:1
        |
    931 | / /// They must remain valid for the duration of the function call.
    932 | |
        | |_
    933 |   #[no_mangle]
    934 | / pub unsafe extern "C" fn drm_panic_qr_generate(
    935 | |     url: *const i8,
    936 | |     data: *mut u8,
    937 | |     data_len: usize,
    ...   |
    940 | |     tmp_size: usize,
    941 | | ) -> u8 {
        | |_______- the comment documents this function
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#empty_line_after_doc_comments
        = note: `-D clippy::empty-line-after-doc-comments` implied by `-D warnings`
        = help: to override `-D warnings` add `#[allow(clippy::empty_line_after_doc_comments)]`
        = help: if the empty line is unintentional remove it

Thus remove the empty line.

Fixes: cb5164a ("drm/panic: Add a QR code panic screen")
Link: rust-lang/rust-clippy#13091 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

drivers/gpu/drm/drm_panic_qr.rs

@@ -929,7 +929,6 @@ impl QrImage<'_> {
 /// * `tmp` must be valid for reading and writing for `tmp_size` bytes.
 ///
 /// They must remain valid for the duration of the function call.
-
 #[no_mangle]
 pub unsafe extern "C" fn drm_panic_qr_generate(
     url: *const i8,