Raw size for large NAND devices (> 4 GB) can exceed 32 bits, so we need
64 bit types as factors. Both factors are of 32 bit types, as such is
the return value. At least one factor needs to be 64 bit type when
calculating the size.

Signed-off-by: Stefan Riedmueller <s.riedmueller@phytec.de>
Signed-off-by: Christian Hemp <c.hemp@phytec.de>
Signed-off-by: Yunus Bas <y.bas@phytec.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>