Fix revision number

In 0002-shared-libs-for-lua.patch, revision number is used to set 
library name:
TO_SOLIB = liblua.so.$(R)

However, library is built using PKG_VERSION which is passed only during
build step:
$(CC) -o $@.$(PKG_VERSION) -shared -Wl,-soname="$@.$(PKG_VERSION)" $?

As a result, dynamic library is not installed in staging or target paths
since bump to lua 5.3.5

So, instead of replacing R by PKG_VERSION and passing this variable in
all steps, simply update R to 5

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

Index: b/Makefile
===================================================================
--- a/Makefile
+++ b/Makefile
@@ -47,6 +47,6 @@

 # Lua version and release.
 V= 5.3
-R= $V.4
+R= $V.5

 # Targets start here.
 all:    $(PLAT)