mtd: nand: qcom: remove memset for clearing read register buffer

The memset in clear_read_regs is overhead. All the register data
will be filled by DMA during NAND operation so making these
register variables zero is not required.

Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>