iio: adc: ad7192: Fix internal/external clock selection

Fix wrong selection of internal clock when mclk is defined.

Resolve a logical inversion introduced in c9ec2cb3.

Fixes: c9ec2cb3 ("iio: adc: ad7192: use devm_clk_get_optional() for mclk")
Signed-off-by: Fabrizio Lamarque <fl.scratchpad@gmail.com>
Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20230530075311.400686-3-fl.scratchpad@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/ad7192.c

@@ -367,7 +367,7 @@ static int ad7192_of_clock_select(struct ad7192_state *st)
 	clock_sel = AD7192_CLK_INT;
 
 	/* use internal clock */
-	if (st->mclk) {
+	if (!st->mclk) {
 		if (of_property_read_bool(np, "adi,int-clock-output-enable"))
 			clock_sel = AD7192_CLK_INT_CO;
 	} else {