Add SPDX GPL-2.0 to numachip.c, which referred to the kernel default
"COPYING" file, which specifies GPL version 2.

Remove the boilerplate language referring to the GPL and "COPYING", relying
on the assertion in b2441318 ("License cleanup: add SPDX GPL-2.0
license identifier to files with no license") that the SPDX identifier may
be used instead of the full boilerplate text.

[bhelgaas: split to separate patch]
Link: https://lore.kernel.org/r/20190828135322.10370-1-kw@linux.comSigned-off-by: Krzysztof Wilczynski <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>