cmd: sf: align erase and write on erase block boundary

cmd: sf: align erase and write on erase block boundary

Align erase and write on erase block boundary in line with how read was
aligned in commit 622b5d35613 ("cmd: sf: Handle unaligned 'update' start
offset").

Fixes: 622b5d35613 ("cmd: sf: Handle unaligned 'update' start offset")
Signed-off-by: Viorel Suman <viorel.suman@nxp.com>
Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Tested-by: Marek Vasut <marek.vasut+renesas@mailbox.org> # R-Car V4H