Use NULL instead of 0 for null pointers

Also fix a misspelled "beginning".

Change-Id: I880ad2fec4dd4ea4866abf34b85e9387c1d6a88d

aom_dsp/grain_table.c

diff --git a/aom_dsp/grain_table.c b/aom_dsp/grain_table.c
index 66c604e..b22752a 100644
--- a/aom_dsp/grain_table.c
+++ b/aom_dsp/grain_table.c
@@ -202,7 +202,7 @@
                                 int64_t end_time, int erase,
                                 aom_film_grain_t *grain) {
   aom_film_grain_table_entry_t *entry = t->head;
-  aom_film_grain_table_entry_t *prev_entry = 0;
+  aom_film_grain_table_entry_t *prev_entry = NULL;
   uint16_t random_seed = grain ? grain->random_seed : 0;
   if (grain) memset(grain, 0, sizeof(*grain));
 
@@ -241,7 +241,7 @@
         entry->end_time = time_stamp;
         if (t->tail == entry) t->tail = new_entry;
       }
-      // If segments aren't aligned, delete from the beggining of subsequent
+      // If segments aren't aligned, delete from the beginning of subsequent
       // segments
       if (end_time > entry_end_time) {
         aom_film_grain_table_lookup(t, entry_end_time, end_time, 1, 0);
@@ -275,12 +275,12 @@
     return error_info->error_code;
   }
 
-  aom_film_grain_table_entry_t *prev_entry = 0;
+  aom_film_grain_table_entry_t *prev_entry = NULL;
   while (!feof(file)) {
     aom_film_grain_table_entry_t *entry = aom_malloc(sizeof(*entry));
     memset(entry, 0, sizeof(*entry));
     grain_table_entry_read(file, error_info, entry);
-    entry->next = 0;
+    entry->next = NULL;
 
     if (prev_entry) prev_entry->next = entry;
     if (!t->head) t->head = entry;