[media] mxl111sf: Fix unintentional garbage stack read

mxl111sf_read_reg takes an address of a variable to write to as an argument.
drivers/media/usb/dvb-usb-v2/mxl111sf-gpio.c:mxl111sf_config_pin_mux_modes
passes several uninitialized stack variables to this routine, expecting
them to be filled in.  In the event that something unexpected happens when
reading from the chip, we end up doing a pr_debug of the value passed in,
revealing whatever garbage happened to be on the stack.

Change the pr_debug to match what happens in the 'success' case, where we
assign buf[1] to *data.

Spotted with Coverity (Bugs 731910 through 731917)

Signed-off-by: Dave Jones <davej@fedoraproject.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Cc: stable@vger.kernel.org
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>