Fix sloppy formatting in instfiles/Makefile.am

Use spaces around = and +=, indent by 2 spaces.

instfiles/Makefile.am

@@ -32,25 +32,25 @@ startscript_DATA = \
 #
 # platform specific files
 #
-SUBDIRS=
+SUBDIRS =
 if LINUX
-SUBDIRS+= \
+SUBDIRS += \
   pam.d \
   pulse
-startscript_DATA+= xrdp.sh
+startscript_DATA += xrdp.sh
 if HAVE_SYSTEMD
 systemdsystemunit_DATA = \
   xrdp-sesman.service \
   xrdp.service
 else
-SUBDIRS+= \
+SUBDIRS += \
   default \
   init.d
 endif # HAVE_SYSTEMD
 endif # LINUX
 
 if FREEBSD
-SUBDIRS+= \
+SUBDIRS += \
   pam.d \
   rc.d \
   pulse