mcelog: fix 'mcelog --client' blocked problem

I found this problem on my x86 box:
$ mcelog --client
Memory errors
SOCKET 1 CHANNEL any DIMM any
corrected memory errors:
	660748032 total
	660748032 in 24h
uncorrected memory errors:
	0 total
	0 in 24h
...
Per page corrected memory statistics:
1000: total 854944 seen "854944 in 24h" offline-failed triggered
done
<blocked here>

I found the "done" command was split to two parts, so the client
don't known when to quit. The strace result is bellow:
$ strace -s 1024 mcelog --client
...
read(4, " total 1 seen \"1 in 24h\" online\n\na0c75f000: total 1 seen \"
1 in 24h\" online\n\na0cdbe000: total 1 seen \"1 in 24h\" online\n\na0d2
e7000: total 1 seen \"1 in 24h\" online\n\na1a3cf000: total 1 seen \"1 in
 24h\" online\n\na1d1ea000: total 1 seen \"1 in 24h\" online\n\na1d673000:
...
3f029000: total 1 seen \"1 in 24h\" online\n\ndo", 1024) = 1024
                                              ^^
read(4, "ne\n", 1024)                   = 3
         ^^^^

In this patch, I used fgets() to read one line string from server each time,
instead of reading 1024 bytes with read().

v2: close fp before return

[AK: Fixed warning]
Signed-off-by: Xie XiuQi <xiexiuqi@huawei.com>
Reviewed-by: Sang Yan <sangyan@huawei.com>
Signed-off-by: Andi Kleen <ak@linux.intel.com>