ubifs: Fix some kernel-doc warnings in gc.c

Fixes the following W=1 kernel build warning(s):

fs/ubifs/gc.c:70: warning: Excess function parameter 'buf' description in 'switch_gc_head'
fs/ubifs/gc.c:70: warning: Excess function parameter 'len' description in 'switch_gc_head'
fs/ubifs/gc.c:70: warning: Excess function parameter 'lnum' description in 'switch_gc_head'
fs/ubifs/gc.c:70: warning: Excess function parameter 'offs' description in 'switch_gc_head'

They're not in use. Remove them.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>

fs/ubifs/gc.c

@@ -57,10 +57,6 @@
 /**
  * switch_gc_head - switch the garbage collection journal head.
  * @c: UBIFS file-system description object
- * @buf: buffer to write
- * @len: length of the buffer to write
- * @lnum: LEB number written is returned here
- * @offs: offset written is returned here
  *
  * This function switch the GC head to the next LEB which is reserved in
  * @c->gc_lnum. Returns %0 in case of success, %-EAGAIN if commit is required,