aarch64: Get rid of a stray double space

The extra space got included as part of the expansion of ELF, which
later interfered with gas-preprocessor which earlier only stripped out
leftover lines starting with '#' if the line started with that char.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/aarch64/asm.S

@@ -23,7 +23,7 @@
 #ifdef __ELF__
 #   define ELF
 #else
-#   define ELF  #
+#   define ELF #
 #endif
 
 #if HAVE_AS_FUNC