hexagon: vdso: Fix build failure

Hexagon images fail to build with the following error.

arch/hexagon/kernel/vdso.c:57:3: error: use of undeclared identifier 'name'
                name = "[vdso]",
                ^

Add the missing '.' to fix the problem.

Fixes: 497258df ("mm: remove legacy install_special_mapping() code")
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Brian Cain <bcain@quicinc.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>