mtd: fix almost all checkpatch warnings in nand_base.c

Only 3 warnings are left, one is off by one character, but splitting the line
would reduce the readability. One is for a for loop statement, which would also
not improve readability. The last one is a false positive on a test.

Artem: it is much easier to verify patches against nand_base.c with
       checkpatch.pl when nand_base.c itself does not have so many
       checkpatch.pl warnings.

Signed-off-by: Florian Fainelli <ffainelli@freebox.fr>
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>