tests: posix: fs: disable CONFIG_EVENTFD

The test doesn't use eventfd so we can disable it to save some space.

Signed-off-by: Kumar Gala <[email protected]>
(cherry picked from commit 70e921d)

Author: galak

tests/posix/fs/prj.conf

@@ -7,3 +7,4 @@ CONFIG_POSIX_API=y
 CONFIG_POSIX_FS=y
 CONFIG_ZTEST=y
 CONFIG_MAIN_STACK_SIZE=4096
+CONFIG_EVENTFD=n