This removes the fat_search_long() in the vfat_add_entry().  This path
is already checked by the vfs layer whether file/directory exists.  So,
we don't need the fat_search_long() in vfat_add_entry().

The following is the result of created the 1000 files,

2.5.39
root@devron (a)[1007]# time ../../create

real    0m2.761s
user    0m0.006s
sys     0m2.752s
root@devron (a)[1008]#

2.5.39 + patch
root@devron (a)[1007]# time ../../create

real    0m1.601s
user    0m0.008s
sys     0m1.575s
root@devron (a)[1008]#