rust: firmware: fix invalid rustdoc link

remove an extra quote from the doc comment so that rustdoc
no longer genertes a link to a nonexistent file.

Signed-off-by: Andrew Ballance <andrewjballance@gmail.com>
Reviewed-by: Danilo Krummrich <dakr@redhat.com>
Acked-by: Miguel Ojeda <ojeda@kernel.org>
Fixes: de658283 ("rust: add firmware abstractions")
Link: https://lore.kernel.org/r/20240709004426.44854-1-andrewjballance@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>