Change min eps value for sgr

This makes sure that all eps values are at least 4 since otherwise
the computation will not fit within 32 bits.

BUG=aomedia:893

Change-Id: I4815a865be8db792d0481172a2dfa0bc0a817f73
diff --git a/av1/common/restoration.c b/av1/common/restoration.c
index 00441f0..0f9c81b 100644
--- a/av1/common/restoration.c
+++ b/av1/common/restoration.c
@@ -34,7 +34,7 @@
 #if MAX_RADIUS == 2
   { 2, 12, 1, 4 },  { 2, 15, 1, 6 },  { 2, 18, 1, 8 },  { 2, 20, 1, 9 },
   { 2, 22, 1, 10 }, { 2, 25, 1, 11 }, { 2, 35, 1, 12 }, { 2, 45, 1, 13 },
-  { 2, 55, 1, 14 }, { 2, 65, 1, 15 }, { 2, 75, 1, 16 }, { 2, 30, 1, 2 },
+  { 2, 55, 1, 14 }, { 2, 65, 1, 15 }, { 2, 75, 1, 16 }, { 2, 30, 1, 6 },
   { 2, 50, 1, 12 }, { 2, 60, 1, 13 }, { 2, 70, 1, 14 }, { 2, 80, 1, 15 },
 #else
   { 2, 12, 1, 4 },  { 2, 15, 1, 6 },  { 2, 18, 1, 8 },  { 2, 20, 1, 9 },