x86/build: Remove leading space in xen.efi.S rule

It happens to be benign, but it causes emacs to ask:

  Suspicious line 194. Save anyway? (y or n)

whenever saving the file.

Fixes: da944a72fd ("x86: split xen-syms/xen.efi linking rules")
Acked-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/Makefile

@@ -191,7 +191,7 @@ ifeq ($(XEN_BUILD_PE),y)
 .$(TARGET).efi.%s.S:
 	$(NM) -pa --format=sysv $< \
 	  | $(objtree)/tools/symbols $(all_symbols) --sysv --sort \
- 	    --source-name=$(TARGET).efi.S \
+	    --source-name=$(TARGET).efi.S \
 	  > $@
 
 # See above for why $(note_file) needs removing here.