cap-v4l: remove unwanted loop in V4L2 mainloop

The while loop would run only once making it useless and leading
to confusion.

So, remove the unwanted while loop and just keep an infinite for
loop.

modules/videoio/src/cap_v4l.cpp

@@ -857,11 +857,6 @@ static int read_frame_v4l2(CvCaptureCAM_V4L* capture) {
 }
 
 static int mainloop_v4l2(CvCaptureCAM_V4L* capture) {
-    unsigned int count;
-
-    count = 1;
-
-    while (count-- > 0) {
     for (;;) {
         fd_set fds;
         struct timeval tv;
@@ -896,7 +891,6 @@ static int mainloop_v4l2(CvCaptureCAM_V4L* capture) {
         if(returnCode == 1)
             return 1;
     }
-    }
     return 0;
 }