mtd: spi-nor: hide jedec_id sysfs attribute if not present

mtd: spi-nor: hide jedec_id sysfs attribute if not present

[ Upstream commit 7d388551b6888f3725e6c957f472526b35161a5b ]

Some non-jedec compliant flashes (like the Everspin flashes) don't have
an ID at all. Hide the attribute in this case.

Fixes: 36ac02286265 ("mtd: spi-nor: add initial sysfs support")
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Link: https://lore.kernel.org/r/20220810220654.1297699-2-michael@walle.cc
Signed-off-by: Sasha Levin <sashal@kernel.org>