UPSTREAM: rtc: lib_test: add MODULE_LICENSE

As the documentation states, "The exact license information can only be
determined via the license information in the corresponding source files."
and the SPDX identifier has the proper information.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Change-Id: Iefa35a688d571fe9c9b744b44941d2cea35781d8
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20210810212008.631359-1-alexandre.belloni@bootlin.com


(cherry picked from commit 5546e3df)
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>