staging: gpib: fix kernel-doc section for write_loop() function

Add a colon character in the kernel-doc section of write_loop() in order
'leng' to be picked as argument by the kernel-doc compiler.

This change fix the following warning:

warning: Function parameter or struct member 'leng' not described in
'send_command'

Signed-off-by: Gaston Gonzalez <gascoar@gmail.com>
Link: https://lore.kernel.org/r/20250305193614.39604-3-gascoar@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>