mtd: maps: vmu-flash: fix typos for struct memcard

Change struct memcard`s element "removeable" -> "removable".

Signed-off-by: Bernard Zhao <bernard@vivo.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200922112814.26761-1-bernard@vivo.com