regmap: using module facilities requires module.h

Commit b33f9cbd ("regmap: Specify a module license") added a
MODULES_LICENSE to this file without adding an include of module.h.

module.h should have been included anyway, since this file has
EXPORT_SYMBOLs as well.  With the pending module.h split up, this would
probably have caused build problems.

Cc: Stephen Warren <swarren@nvidia.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>