uwb: Add export.h for EXPORT_SYMBOL/THIS_MODULE as required

These macros are no longer in module.h and module.h is no longer
present everywhere.  Call out export.h for the real users who
are making use of these macros, or else we'll get things like:

 CC      drivers/uwb/umc-drv.o
drivers/uwb/umc-dev.c:42: warning: data definition has no type or storage class
drivers/uwb/umc-dev.c:42: warning: type defaults to ‘int’ in declaration of ‘EXPORT_SYMBOL_GPL’
drivers/uwb/umc-dev.c:42: warning: parameter names (without types) in function declaration

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>