checkasm: aarch64: Specify alignment for the register_init const array

Loads from this strictly doesn't require alignment, but specify it
just for consistency with the arm version.
Signed-off-by: Martin Storsjö <martin@martin.st>

tests/checkasm/aarch64/checkasm.S

@@ -22,7 +22,7 @@
 
 #include "libavutil/aarch64/asm.S"
 
-const register_init
+const register_init, align=4
     .quad 0x21f86d66c8ca00ce
     .quad 0x75b6ba21077c48ad
     .quad 0xed56bb2dcb3c7736