docs: driver-api: firmware: fallback-mechanisms: Fix rendering of bullet point

Without this patch, the "Firmware is not accessible [...]" line is
rendered in bold, which does not seem intentional.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20200905184131.1280337-1-j.neuschaefer@gmx.netSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/driver-api/firmware/fallback-mechanisms.rst

@@ -42,6 +42,7 @@ fallback mechanism:
   supported for request_firmware_into_buf().
 
 * Firmware is not accessible through typical means:
+
         * It cannot be installed into the root filesystem
         * The firmware provides very unique device specific data tailored for
           the unit gathered with local information. An example is calibration