Try to read firmware image before prompting the user to confirm

firmware download.  This correctly prints an error and exits for
an incorrect firmware image name before prompting the user to
confirm the download.

Sponsored by:	Intel
MFC after:	3 days

sbin/nvmecontrol/firmware.c

@@ -253,6 +253,9 @@ firmware(int argc, char *argv[])
 		    "of available images\n",
 		    slot, controller);
 
+	if (f_flag)
+		read_image_file(image, &buf, &size);
+
 	if (f_flag && a_flag)
 		printf("You are about to download and activate "
 		       "firmware image (%s) to controller %s.\n"
@@ -282,7 +285,6 @@ firmware(int argc, char *argv[])
 	}
 
 	if (f_flag) {
-		read_image_file(image, &buf, &size);
 		update_firmware(fd, buf, size);
 		if (a_flag)
 			activate_firmware(fd, slot,