staging: logger: fix build error due to removed ki_nbytes

staging: logger: fix build error due to removed ki_nbytes

This patch fixes build error. Logger driver was removed
from mainline kernel and after that there was some changes and
one of them is that ki_nbytes member was removed from kiocb structure.
	66ee59a fs: remove ki_nbytes

This patch makes count member of iov_iter structure to be used instead.

Change-Id: I11e9ebdac7dd86c02fd692a67562a23e5c685f69
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Karol Lewandowski <k.lewandowsk@samsung.com>