[media] kernel:kfifo: export __kfifo_max_r symbol

kfifo_avail expands to __kfifo_max_r which is not an exported symbol.
Any kernel module using kfifo_avail will result in build failures
because of this.
This patch just exports __kfifo_max_r symbol to fix such problems in
future.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@st.com>
Acked-by: Stefani Seibold <stefani@seibold.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

kernel/kfifo.c

@@ -402,6 +402,7 @@ unsigned int __kfifo_max_r(unsigned int len, size_t recsize)
 		return max;
 	return len;
 }
+EXPORT_SYMBOL(__kfifo_max_r);
 
 #define	__KFIFO_PEEK(data, out, mask) \
 	((data)[(out) & (mask)])