Set dev_name to default device name

If no device is specified with the --device flag, set dev_name to the id of
the first device.

Before, if the --device flag is not used to specify the default device, the
dev pointer was set to first device found (see commit
c9140d1e5070dae2746d3b70c0390075bd5380f6), but the dev_name pointer was
left set to NULL.  As a result, some error messages did not print the name
of the default device:

    % brightnessctl -s
    Error saving device data: No such file or directory
    Could not save data for device '(null)'.
    Device 'intel_backlight' of class 'backlight':
            Current brightness: 1000 (20%)
            Max brightness: 4794

    % brightnessctl -s -m
    Error saving device data: No such file or directory
    Could not save data for device '(null)'.
    intel_backlight,backlight,1000,20%,4794
    %

After this commit, all error messages have the correct name:

    % brightnessctl -s
    Error saving device data: No such file or directory
    Could not save data for device 'intel_backlight'.
    Device 'intel_backlight' of class 'backlight':
            Current brightness: 1000 (20%)
            Max brightness: 4794

    % brightnessctl -s -m
    Error saving device data: No such file or directory
    Could not save data for device 'intel_backlight'.
    intel_backlight,backlight,1000,20%,4794
    %

1 files changed, 2 insertions, 2 deletions

diff --git a/brightnessctl.c b/brightnessctl.c
index 60ca3a4..d6170e9 100644
--- a/brightnessctl.c
+++ b/brightnessctl.c
@@ -151,6 +151,8 @@ int main(int argc, char **argv) {
 		return list_devices(devs);
 	}
 	dev_name = p.device;
+	if (!dev_name)
+		dev_name = devs[0]->id;
 	if (argc == 0)
 		p.operation = GET;
 	else switch (argv[0][0]) {
@@ -242,8 +244,6 @@ int parse_value(struct value *val, char *str) {
 
 struct device *find_device(struct device **devs, char *name) {
 	struct device *dev;
-	if (!name)
-		return *devs;
 	while ((dev = *(devs++)))
 		if (!strcmp(dev->id, name))
 			return dev;