Fix invalid operator in dash

Some shells, like dash, don't support [ x == x ], reporting invalid syntax,
and silently failing.

--- gputils-1.5.2.orig/doc/html-help/Makefile.am
+++ gputils-1.5.2/doc/html-help/Makefile.am
@@ -7,7 +7,7 @@
 pkgdatadir = @GPUTILS_HTMLDOC_PATH@
 
 html-doc:
-	if [ "$(ENABLE_HTML_DOC)" == "yes" ]; then \
+	if [ "$(ENABLE_HTML_DOC)" = "yes" ]; then \
 	  if [ ! -e $(DEFAULT_MPLABX_PATH)/mpasmx/8bit_device.info ]; then \
 	    @echo "Can't find mplabx installation; HTML documentation will not be built."; \
 	  else \
@@ -18,7 +18,7 @@
 install: install-html
 
 install-html:
-	if [ "$(ENABLE_HTML_DOC)" == "yes" ]; then \
+	if [ "$(ENABLE_HTML_DOC)" = "yes" ]; then \
 	  if [ -n "$$(ls *.html 2>/dev/null)" -a -n "$$(ls *.css 2>/dev/null)" ]; then \
 	    $(install_sh) -d "$(DESTDIR)$(pkgdatadir)"; \
 	    $(install_sh) -c -m 644 *.css *.html "$(DESTDIR)$(pkgdatadir)"; \