regmap: mmio: Add missing MODULE_DESCRIPTION()

There were already several commits to add module descriptions to regmap
modules. But this one was still missing:

WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/base/regmap/regmap-mmio.o

Signed-off-by: Luis Henriques <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/base/regmap/regmap-mmio.c

···
 }
 EXPORT_SYMBOL_GPL(regmap_mmio_detach_clk);
 
+MODULE_DESCRIPTION("regmap MMIO Module");
 MODULE_LICENSE("GPL v2");