staging: r8188eu: remove unused ijk_matrix_regs_set implementation

Instance IQKMatrixRegSetting of struct ijk_matrix_regs_set is
initialised and its member variables are assigned values, but it is
not used anywhere. Remove the structure and its unused implementation.

Suggested-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Deepak R Varma <drv@mailo.com>
Link: https://lore.kernel.org/r/Y2P6Jj+IcPss0wFd@qemulion


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