mtd-utils: nandwrite: Clarify usage of aligned "erasesize"

mtd-utils: nandwrite: Clarify usage of aligned "erasesize"

Due to the presence of the "--block-align" flag, nandwrite uses a
blocksize throughout that, depeding on the execution parameters, may
not be the actual erasesize of the NAND flash. In order to clarify
this situation for the untrained viewer of nandwrite's code, we should
not change the value of "meminfo.erasesize" itself; rather, we can
utilize a separate, calculated "ebsize_aligned". Then, when a user
actually wants to refer to the physical erasesize, it's straightforward.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>