rpm_log: Fix file_read error

Issue:
cat /d/rpm_log
sh: cat: /d/rpm_log: Try again

The change was incorrect pushed without braces around if statement.
Return -EAGAIN only if the file permission is O_NON_BLOCK or there
is nothing in the log buf.

Change-Id: Id7a549c223aad86185da928b2592c8de02e87623
Signed-off-by: Archana Sathyakumar <asathyak@codeaurora.org>