media: imx274: fix stack corruption in imx274_read_reg

imx274_read_reg() takes a u8 pointer ("reg") and casts it to pass it
to regmap_read(), which takes an unsigned int pointer. This results in
a corrupted stack and random crashes.

Fixes: 0985dd30 ("media: imx274: V4l2 driver for Sony imx274 CMOS sensor")

Cc: stable@vger.kernel.org # for 4.15 and up
Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>