nvmem: rmem: fix undefined reference to memremap

nvmem: rmem: fix undefined reference to memremap

Fix below error reporte by kernel test robot
rmem.c:(.text+0x14e): undefined reference to memremap
s390x-linux-gnu-ld: rmem.c:(.text+0x1b6): undefined reference to memunmap

Fixes: 5a3fa75a4d9c ("nvmem: Add driver to expose reserved memory as nvmem")
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210330111241.19401-9-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>