Install missing default_coef_probs.h

Make sure that this header is listed as one of the sources, so that it
will be installed if necessary.

Change-Id: I2427e494488126b179151dc21043c1e2c8ba5991

vp8/vp8_common.mk

@@ -19,6 +19,7 @@ VP8_COMMON_SRCS-yes += common/asm_com_offsets.c
 VP8_COMMON_SRCS-yes += common/blockd.c
 VP8_COMMON_SRCS-yes += common/coefupdateprobs.h
 VP8_COMMON_SRCS-yes += common/debugmodes.c
+VP8_COMMON_SRCS-yes += common/default_coef_probs.h
 VP8_COMMON_SRCS-yes += common/entropy.c
 VP8_COMMON_SRCS-yes += common/entropymode.c
 VP8_COMMON_SRCS-yes += common/entropymv.c