mtd: spi-nor: fix select_uniform_erase to skip 0 erase size

4bait will set the erase size to 0 if there is no corresponding
opcode for the 4byte erase. Fix spi_nor_select_uniform_erase to skip
the 0 erase size to avoid mtd device registration failure cases.

Reported-by: Jae Hyun Yoo <quic_jaehyoo@quicinc.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Link: https://lore.kernel.org/r/20220810220654.1297699-6-michael@walle.cc