drm/panic: add missing space

Add missing space in sentence.

This was found using the Clippy `doc_markdown` lint, which we may want
to enable.

Fixes: cb5164ac43d0 ("drm/panic: Add a QR code panic screen")
Signed-off-by: Miguel Ojeda <[e-mail]>
Reviewed-by: Jocelyn Falempe <[e-mail]>
Reviewed-by: Benno Lossin <[e-mail]>
Signed-off-by: Jocelyn Falempe <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/gpu/drm/drm_panic_qr.rs

···
 //! It is called from a panic handler, so it should't allocate memory and
 //! does all the work on the stack or on the provided buffers. For
 //! simplification, it only supports low error correction, and applies the
-//! first mask (checkerboard). It will draw the smallest QRcode that can
+//! first mask (checkerboard). It will draw the smallest QR code that can
 //! contain the string passed as parameter. To get the most compact
 //! QR code, the start of the URL is encoded as binary, and the
 //! compressed kmsg is encoded as numeric.