modules: remove bashism

It Fixes OS/2 compilation.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/common.am

@@ -15,7 +15,7 @@ CLEANFILES = $(BUILT_SOURCES)
 LTLIBVLCCORE = $(top_builddir)/src/libvlccore.la
 
 # Module name from object or executable file name.
-MODULE_NAME = $$(p="$@"; p="$${p\#\#*/}"; p="$${p\#lib}"; p="$${p%_plugin*}"; p="$${p//-/\_}"; p="$${p%.lo}"; echo "$$p")
+MODULE_NAME = $$(p="$@"; p="$${p\#\#*/}"; p="$${p\#lib}"; p="$${p%_plugin*}"; p=$$(echo "$$p"|sed 's/-/_/g'); p="$${p%.lo}"; echo "$$p")
 
 AM_CPPFLAGS = -DMODULE_STRING=\"$(MODULE_NAME)\"
 if HAVE_DYNAMIC_PLUGINS