git-mtd: symbol_get() fix

drivers/mtd/devices/docprobe.c: In function `DoC_Probe':
drivers/mtd/devices/docprobe.c:338: warning: assignment from incompatible pointer type
drivers/mtd/devices/docprobe.c:341: warning: assignment from incompatible pointer type

Cc: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>