arm64/signal: Don't redundantly verify FPSIMD magic

We validate that the magic in the struct fpsimd_context is correct in
restore_fpsimd_context() but this is redundant since parse_user_sigframe()
uses this magic to decide to call the function in the first place. Remove
the extra validation.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20221212-arm64-signal-cleanup-v3-1-4545c94b20ff@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/signal.c

@@ -191,15 +191,14 @@ static int preserve_fpsimd_context(struct fpsimd_context __user *ctx)
 static int restore_fpsimd_context(struct fpsimd_context __user *ctx)
 {
 	struct user_fpsimd_state fpsimd;
-	__u32 magic, size;
+	__u32 size;
 	int err = 0;
 
-	/* check the magic/size information */
-	__get_user_error(magic, &ctx->head.magic, err);
+	/* check the size information */
 	__get_user_error(size, &ctx->head.size, err);
 	if (err)
 		return -EFAULT;
-	if (magic != FPSIMD_MAGIC || size != sizeof(struct fpsimd_context))
+	if (size != sizeof(struct fpsimd_context))
 		return -EINVAL;
 
 	/* copy the FP and status/control registers */