media: i2c: imx290: Simplify error handling when writing registers

Error handling for register writes requires checking the error status of
every single write. This makes the code complex, or incorrect when the
checks are omitted. Simplify this by passing a pointer to an error code
to the imx290_write_reg() function, which allows writing multiple
registers in a row and only checking for errors at the end.

While at it, rename imx290_write_reg() to imx290_write() as there's
nothing else than registers to write, and rename imx290_read_reg()
accordingly.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>