media: camss: csiphy-3ph: avoid undefined behavior

Marking a case of the switch statement as unreachable means the
compiler treats it as undefined behavior, which is then caught by
an objtool warning:

drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.o: warning: objtool: csiphy_lanes_enable() falls through to next function csiphy_lanes_disable()

Instead of simply continuing execution at a random place of the
driver, print a warning and return from to the caller, which
makes it possible to understand what happens and avoids the
warning.

Fixes: 53655d2a ("media: camss: csiphy-3ph: add support for SM8250 CSI DPHY")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c

@@ -429,7 +429,8 @@ static void csiphy_gen2_config_lanes(struct csiphy_device *csiphy,
 		array_size = ARRAY_SIZE(lane_regs_sm8250[0]);
 		break;
 	default:
-		unreachable();
+		WARN(1, "unknown cspi version\n");
+		return;
 	}
 
 	for (l = 0; l < 5; l++) {