util: Add 'static' attribute to function implementation

The static code analyzer smatch complains because of a missing 'static'
attribute:

util/module.c:166:6: warning:
 symbol 'module_load' was not declared. Should it be static?

'static' is used in the forward declaration, but not in the implementation.
Add it there, too.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>