qmp: Use generic errors in memchar-read, memchar-write

New errors should be generic unless there's a real use case for rich
errors.
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

qapi-schema.json

@@ -352,7 +352,6 @@
 #          by default is 'utf8'.
 #
 # Returns: Nothing on success
-#          If @device is not a valid char device, DeviceNotFound
 #
 # Since: 1.4
 ##
@@ -374,7 +373,6 @@
 #          memchardev, by default is 'utf8'.
 #
 # Returns: data read from the device
-#          If @device is not a valid memchr device, DeviceNotFound
 #
 # Since: 1.4
 ##

qemu-char.c

@@ -2764,7 +2764,7 @@ void qmp_memchar_write(const char *device, const char *data,
 
     chr = qemu_chr_find(device);
     if (!chr) {
-        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        error_setg(errp, "Device '%s' not found", device);
         return;
     }
 
@@ -2799,7 +2799,7 @@ char *qmp_memchar_read(const char *device, int64_t size,
 
     chr = qemu_chr_find(device);
     if (!chr) {
-        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        error_setg(errp, "Device '%s' not found", device);
         return NULL;
     }