media: Fix raw video format comments

The "PN" subscript in PIXEL_FORMAT_YUVxxxPN formats are not
indicating the bits per pixel, but indicating the
nubmer of bits per pixel component/channel.
For eg: PIXEL_FORMAT_YUV420P10 is mapped to the ffmpeg
format AV_PIX_FMT_YUV420P10LE and this is not a 10bits per pixel
format, it has 15 bits in each pixel.

R=dalecurtis@chromium.org

Change-Id: Idafc9a3b8d1188154610638ce4db02964586aeb8
Reviewed-on: https://chromium-review.googlesource.com/c/1292819
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607146}

AUTHORS

@@ -820,6 +820,7 @@ Sooho Park <sooho1000@gmail.com>
 Soojung Choi <crystal2840@gmail.com>
 Soorya R <soorya.r@samsung.com>
 Soren Dreijer <dreijerbit@gmail.com>
+Sreerenj Balachandran <sreerenj.balachandran@intel.com>
 Srirama Chandra Sekhar Mogali <srirama.m@samsung.com>
 Staphany Park <stapark008@gmail.com>
 Stephen Searles <stephen.searles@gmail.com>

media/base/video_types.h

@@ -53,8 +53,9 @@ enum VideoPixelFormat {
   // Plane size = Row pitch * (((height+31)/32)*32)
   PIXEL_FORMAT_MT21 = 15,
 
-  // The P* in the formats below designates the number of bits per pixel. I.e.
-  // P9 is 9-bits per pixel, P10 is 10-bits per pixel, etc.
+  // The P* in the formats below designates the number of bits per pixel
+  // component. I.e. P9 is 9-bits per pixel component, P10 is 10-bits per pixel
+  // component, etc.
   PIXEL_FORMAT_YUV420P9 = 16,
   PIXEL_FORMAT_YUV420P10 = 17,
   PIXEL_FORMAT_YUV422P9 = 18,