selftests/powerpc: Remove repeated word in comments

Remove the repeated word "not" in comments.

Signed-off-by: Shaomin Deng <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

tools/testing/selftests/powerpc/include/pkeys.h

···
 #undef PKEY_DISABLE_EXECUTE
 #define PKEY_DISABLE_EXECUTE	0x4
 
-/* Older versions of libc do not not define this */
+/* Older versions of libc do not define this */
 #ifndef SEGV_PKUERR
 #define SEGV_PKUERR	4
 #endif