include/linux/eventfd.h: fix incorrect filename is a comment

Comment in eventfd.h referred to 'include/asm-generic/fcntl.h'
while the correct path is 'include/uapi/asm-generic/fcntl.h'.

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>