[MTD] [NAND] make oobavail public

During the MTD rework the oobavail parameter of mtd_info structure has become
private. This is not quite correct in terms of integrity and logic. If we have
means to write to OOB area, then we'd like to know upfront how many bytes out
of OOB are spare per page to be able to adapt to specific cases.
The patch inlined adds the public oobavail parameter.

Signed-off-by: Vitaly Wool <vwool@ru.mvista.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

include/linux/mtd/mtd.h

@@ -121,6 +121,7 @@ struct mtd_info {
 	u_int32_t writesize;
 
 	u_int32_t oobsize;   // Amount of OOB data per block (e.g. 16)
+	u_int32_t oobavail;  // Available OOB bytes per block
 
 	// Kernel-only stuff starts here.
 	char *name;