Cosmetics: Fix indentation.

Found by: Alexander Strasser

libavcodec/pnm.c

@@ -113,9 +113,9 @@ int ff_pnm_decode_header(AVCodecContext *avctx, PNMContext * const s)
         if (depth == 1) {
             if (maxval == 1) {
                 avctx->pix_fmt = PIX_FMT_MONOWHITE;
-           } else if (maxval == 255) {
+            } else if (maxval == 255) {
                 avctx->pix_fmt = PIX_FMT_GRAY8;
-           } else {
+            } else {
                 avctx->pix_fmt = PIX_FMT_GRAY16BE;
             }
         } else if (depth == 3) {