openrisc: Refactor 16-bit constant relocation

arch/openrisc/kernel/module.c: In function 'apply_relocate_add':
arch/openrisc/kernel/module.c:50:13: warning: assignment from incompatible pointer type
arch/openrisc/kernel/module.c:54:13: warning: assignment from incompatible pointer type

Move the pointer increments to the dereference statements to avoid
incompatible pointer assignments, and remove superfluous casts.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jonas Bonn <jonas@southpole.se>