mtd: rawnand: brcmnand: improve hamming oob layout

The current code generates 8 oob sections:
S1	1-5
ECC	6-8
S2	9-15
S3	16-21
ECC	22-24
S4	25-31
S5	32-37
ECC	38-40
S6	41-47
S7	48-53
ECC	54-56
S8	57-63

Change it by merging continuous sections:
S1	1-5
ECC	6-8
S2	9-21
ECC	22-24
S3	25-37
ECC	38-40
S4	41-53
ECC	54-56
S5	57-63

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200512075733.745374-3-noltari@gmail.com