hw/9pfs: Fix broken compilation caused by wrong trace events

hw/9pfs: Fix broken compilation caused by wrong trace events

Commit c572f23a3e7180dbeab5e86583e43ea2afed6271 added trace events
with mismatching format string and arguments.

gcc reports these errors:

In file included from trace.c:2:0:
trace.h: In function ‘trace_v9fs_attach’:
trace.h:2850:9: error: too many arguments for format [-Werror=format-extra-args]
trace.h: In function ‘trace_v9fs_wstat’:
trace.h:3039:9: error: too many arguments for format [-Werror=format-extra-args]
trace.h: In function ‘trace_v9fs_mkdir’:
trace.h:3088:9: error: too many arguments for format [-Werror=format-extra-args]
trace.h: In function ‘trace_v9fs_mkdir_return’:
trace.h:3095:9: error: too many arguments for format [-Werror=format-extra-args]

Fix the format strings and also use %u instead of %d for unsigned values
in the changed strings. There are more minor errors of this kind
which I did not fix because that would make the review more difficult.

v2: Fixed position of } for v9fs_mkdir_return.

Cc: Harsh Prateek Bora <harsh@linux.vnet.ibm.com>
Signed-off-by: Stefan Weil <sw@weilnetz.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>