mtd: nand: omap: ecc.calculate: rename omap3_calculate_ecc_bch to omap_calculate_ecc_bch

rename omap3_calculate_ecc_bch -> omap_calculate_ecc_bch to
keep nomenclature independent of any device family.

Tested-by: Stefan Roese <sr@denx.de>
Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>