various: fix typos

usefull -> useful
seperately -> separately
reciever -> receiver

Signed-off-by: Clément Péron <peron.clem@gmail.com>

doc/filters.texi

@@ -14547,7 +14547,7 @@ e.g. quality comparison.
 
 Each line of the map file must contain three items per input frame, the input
 PTS (decimal), the output PTS (decimal) and the
-output TIMEBASE (decimal/decimal), seperated by a space.
+output TIMEBASE (decimal/decimal), separated by a space.
 This file format corresponds to the output
 of @code{-stats_mux_pre_fmt="@{ptsi@} @{pts@} @{tb@}"}.
 

libavdevice/avfoundation.m

@@ -150,7 +150,7 @@ static void unlock_frames(AVFContext* ctx)
     pthread_mutex_unlock(&ctx->frame_lock);
 }
 
-/** FrameReciever class - delegate for AVCaptureSession
+/** FrameReceiver class - delegate for AVCaptureSession
  */
 @interface AVFFrameReceiver : NSObject
 {
@@ -242,7 +242,7 @@ static void unlock_frames(AVFContext* ctx)
 
 @end
 
-/** AudioReciever class - delegate for AVCaptureSession
+/** AudioReceiver class - delegate for AVCaptureSession
  */
 @interface AVFAudioReceiver : NSObject
 {

libavfilter/vf_nlmeans_opencl.c

@@ -207,7 +207,7 @@ static int nlmeans_plane(AVFilterContext *avctx, cl_mem dst, cl_mem src,
             }
         }
     }
-    // repack dx/dy seperately, as we want to do four pairs of dx/dy in a batch
+    // repack dx/dy separately, as we want to do four pairs of dx/dy in a batch
     for (i = 0; i < nb_pixel / 4; i++) {
         dxdy[i * 8] = tmp[i * 8];         // dx0
         dxdy[i * 8 + 1] = tmp[i * 8 + 2]; // dx1

libavformat/mxfenc.c

@@ -2682,7 +2682,7 @@ static int mxf_parse_jpeg2000_frame(AVFormatContext *s, AVStream *st, AVPacket *
         return AVERROR_INVALIDDATA;
     }
 
-    /* Extract usefull size information from the SIZ marker */
+    /* Extract useful size information from the SIZ marker */
     if (bytestream2_get_be16u(&g) != JPEG2000_SIZ) {
         av_log(s, AV_LOG_ERROR, "Mandatory SIZ marker is not present\n");
         return AVERROR_INVALIDDATA;