9pfs: fix bug of reading host directory path

9pfs: fix bug of reading host directory path

On Windows host, if the user selected the root directory as Host
Directory Sharing path, the emulator launching failure could occur.

There was a code that remove the last backslash of entered path on
Windows implementation. By the way, stat() function could not read the
path when root path like 'c:\' had entered and been removed the last
backslash(the result was 'c:').
So we change the code to remove the backslash only if the entered path
is not a root directory.

We should check the stat() working mechanism about reading pathes
including backslash on Windows later.

Change-Id: I7a155520af1f008f927e6dc67408e930c0f73ab1
Signed-off-by: ChulHo Song <ch81.song@samsung.com>
Signed-off-by: Sooyoung Ha <yoosah.ha@samsung.com>
(cherry picked from commit 20be828e348259146208ee67f13c1b340a8eaff8)