file.c: Fix a file descriptor leak in readfile()

In file.c::readfile() the file was being opened once at fd declaration
time and then again a few lines later and only being closed once. Remove
the open() at fd declaration time leaving the later one where the fd check
is done.

Signed-off-by: Andrew Clayton <andrew@digital-domain.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>