ANDROID: rename struct task_struct.in_eventfd to fix ABI

In commit f8e80792 ("eventfd: guard wake_up in eventfd fs calls as
well"), the field in_eventfd_signal in struct task_struct was renamed to
in_eventfd which breaks the stable kernel ABI in android.  Rename it
back to preserve the ABI.

Bug: 161946584
Fixes: f8e80792 ("eventfd: guard wake_up in eventfd fs calls as well")
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: If076bdc4baa3a460c9512403c8f4ea1da8848a13