avutil: actually install hash.h

This header is designed as a public header (with APIchanges entry and
everything), but it is forgotten to put into the headers to be installed
list.

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/Makefile

@@ -26,6 +26,7 @@ HEADERS = adler32.h                                                     \
           fifo.h                                                        \
           file.h                                                        \
           frame.h                                                       \
+          hash.h                                                        \
           hmac.h                                                        \
           imgutils.h                                                    \
           intfloat.h                                                    \