aarch64: Use the correct syntax for relocations

This fixes building in PIC mode with gas. The examples in the gas
manual showed using a # here even though gas itself actually didn't
support that syntax (and the gas test suite only tests it without
the extra hash sign).

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>

libavutil/aarch64/asm.S

@@ -58,8 +58,8 @@ ELF     .size   \name, . - \name
 
 .macro  movrel rd, val
 #if CONFIG_PIC
-        adrp            \rd, #:pg_hi21:\val
-        add             \rd, \rd, #:lo12:\val
+        adrp            \rd, :pg_hi21:\val
+        add             \rd, \rd, :lo12:\val
 #else
         ldr             \rd, =\val
 #endif