mtd: ubi: eba: Fix a couple of misdocumentation issues

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

 drivers/mtd/ubi/eba.c:1304: warning: Function parameter or member 'vidb' not described in 'ubi_eba_copy_leb'
 drivers/mtd/ubi/eba.c:1304: warning: Excess function parameter 'vid_hdr' description in 'ubi_eba_copy_leb'
 drivers/mtd/ubi/eba.c:1483: warning: Function parameter or member 'ai' not described in 'print_rsvd_warning'

Cc: Richard Weinberger <richard@nod.at>
Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: linux-mtd@lists.infradead.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20201109182206.3037326-12-lee.jones@linaro.org