input: touchscreen: ft8719_spi_c3j: fix pointer comparison

Fix pointer to null char constant comparison

+++++++++++++++++++++++++++++++++++++++
Build error:

drivers/input/touchscreen/ft8719_spi_c3j/focaltech_test/focaltech_test_ini.c:122:15:
warning: comparing a pointer to a null character constant; did you mean
to compare to NULL? [-Wpointer-compare]
  122 |                 if  ((cs == '\0') || (ct == '\0'))
      |                             ^~~~
      |                             (void *)0
drivers/input/touchscreen/ft8719_spi_c3j/focaltech_test/focaltech_test_ini.c:122:31:
warning: comparing a pointer to a null character constant; did you mean
to compare to NULL? [-Wpointer-compare]
  122 |                 if  ((cs == '\0') || (ct == '\0'))
      |                                             ^~~~
      |                                             (void *)0
+++++++++++++++++++++++++++++++++++++++

Change-Id: I3da858fb1569493fcd829d3894ef4624d9c8bf06
Reviewed-on: https://gerrit.mot.com/1687857


SLTApproved: Slta Waiver
SME-Granted: SME Approvals Granted
Tested-by: Jira Key
Reviewed-by: Konstantin Makariev <kmakariev@motorola.com>
Reviewed-by: Rafael Ortolan <rafones@motorola.com>
Submit-Approved: Sergio Vilela <sv008@motorola.com>
Reviewed-on: https://gerrit.mot.com/1761150


Reviewed-by: Jianqi Yang <yangj@motorola.com>
Submit-Approved: Jira Key