fs/dcache.c: Fix the too small buffer for dname

temp[64] is used for internal temporary buffer in dynamic_dname().
This
is for dname. But It's too small. dname's size may be > 64.
In that
case, it returns as -ENAMETOOLONG. So Increase the buffer size
to 256
for avoiding this issue.

The following was caused by the small
buffer.
WARNING: at /kernel/mm/page_alloc.c:2470
__alloc_pages_nodemask+0x24c/0x938()
CPU: 2 PID: 505 Comm: android.bg
Not tainted 3.10.0-g2f73780-00003-g2ff41d9-dirty #13
[<c010ba3c>]
(unwind_backtrace+0x0/0x11c) from [<c0109cac>]
(show_stack+0x10/0x14)
[<c0109cac>] (show_stack+0x10/0x14) from
[<c01939a0>] (warn_slowpath_common+0x48/0x68)
[<c01939a0>]
(warn_slowpath_common+0x48/0x68) from [<c0193a7c>]
(warn_slowpath_null+0x18/0x20)
[<c0193a7c>]
(warn_slowpath_null+0x18/0x20) from [<c0222454>]
(__alloc_pages_nodemask+0x24c/0x938)
[<c0222454>]
(__alloc_pages_nodemask+0x24c/0x938) from [<c0222b50>]
(__get_free_pages+0x10/0x24)
[<c0222b50>] (__get_free_pages+0x10/0x24)
from [<c024faf8>] (kmalloc_order_trace+0x24/0xf0)
[<c024faf8>]
(kmalloc_order_trace+0x24/0xf0) from [<c024fe20>]
(__kmalloc+0x30/0x244)
[<c024fe20>] (__kmalloc+0x30/0x244) from
[<c02723c8>] (seq_read+0x270/0x464)
[<c02723c8>] (seq_read+0x270/0x464)
from [<c0256a18>] (vfs_read+0xa4/0x134)
[<c0256a18>]
(vfs_read+0xa4/0x134) from [<c0256de8>]
(SyS_read+0x38/0x68)
[<c0256de8>] (SyS_read+0x38/0x68) from [<c0106140>]
(ret_fast_syscall+0x0/0x30)

Change-Id:
I74f5217ba3c4be73e91f33f900f1f0c26810cc05
Signed-off-by: Devin Kim
<dojip.kim@lge.com>
Signed-off-by: franciscofranco
<franciscofranco.1990@gmail.com>

idea is taken here -
https://github.com/franciscofranco/hammerhead/commit/a652d8f6d6f21ff59cffda32496a9e4fd2d10113