checkpatch: prefer MODULE_LICENSE("GPL") over MODULE_LICENSE("GPL v2")

checkpatch: prefer MODULE_LICENSE("GPL") over MODULE_LICENSE("GPL v2")

There is no effective difference.

Given the large number of uses of "GPL v2", emit this message only for
patches as a trivial treeside sed could be done one day.

Ref: commit bf7fbeeae6db ("module: Cure the MODULE_LICENSE "GPL" vs. "GPL v2" bogosity")

Link: https://lkml.kernel.org/r/20220128185924.80137-1-joe@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Cc: Dwaipayan Ray <dwaipayanray1@gmail.com>
Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>