arm64: fix padding computation in struct ucontext

The expression to compute the padding needed to fill the uc_sigmask field
to 1024 bits actually computes the padding needed for 1080 bits.
Fortunately, due to the 16-byte alignment of the following field
(uc_mcontext) the definition in glibc contains enough bytes of padding
after uc_sigmask so that the overall offsets and size match in both
definitions.
Signed-off-by: Andreas Schwab <schwab@suse.de>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/ucontext.h

@@ -22,7 +22,7 @@ struct ucontext {
 	stack_t		  uc_stack;
 	sigset_t	  uc_sigmask;
 	/* glibc uses a 1024-bit sigset_t */
-	__u8		  __unused[(1024 - sizeof(sigset_t)) / 8];
+	__u8		  __unused[1024 / 8 - sizeof(sigset_t)];
 	/* last for future expansion */
 	struct sigcontext uc_mcontext;
 };